Environmentally Focused Patterning and Processing of Polymer Thin Films
by Initiated Chemical Vapor deposition (iCVD) and Oxidative Chemical
Vapor Deposition (oCVD)
MASSACHUSETTS INSTITE
OF TECHNOLOGY
by
Nathan J. Trujillo
SEP 16 2010
M.S. Chemical Engineering Practice
Massachusetts Institute of Technology, Cambridge MA (2009)
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B.S. Chemical Engineering
University of California, San Diego, La Jolla CA (2005)
Submitted to the Department of Chemical Engineering
in Partial Fulfillment of the Requirements for the Degree of
DOCTOR OF PHILOSOPHY IN CHEMICAL ENGINEERING PRACTICE
AT THE
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
May 2010
D 2010 Massachusetts Institute of Technology. All rights reserved.
Signature of Author: .
Department of Chemical Engineering
May, 2010
Certified by:
.................
Karen K. Gleason
Professor of Chemical Engineering
Thesis Supervisor
Accepted by: ...................................................
William M. Deen
Professor of Chemical Engineering
Chairman, Committee for Graduate Students
Environmentally Focused Patterning and Processing of Polymer Thin Films by Initiated
Chemical Vapor Deposition (iCVD) and Oxidative Chemical Vapor Depositon (oCVD)
by
Nathan J. Trujillo
Submitted to the Department of Chemical Engineering
on October 19, 2009 in Partial Fulfillment of the
Requirements for the Degree of
Doctor of Philosophy in Chemical Engineering Practice
ABSTRACT
The new millennium has brought fourth many technological innovations made possible
by the advancement of high speed integrated circuits. The materials and energy requirements for
a microchip is orders of magnitude higher than that of "traditional" goods, and current materials
management requirements for EHS friendly low-k processing require a 10% annual increase in
raw materials utilization.
Initiated Chemical Vapor Deposition (iCVD) is a low-energy, one step, solvent-free
process for producing polymeric thin films This thesis describes the deposition of a novel low-k
iCVD precursor, 1,3,5,7-tetravinyltetramethylcylcotetrasiloxane (V4D4). The high degree of
organic content in the as-deposited film affords the ability to tune the film's properties by
annealing. The incorporation of atmospheric oxygen at high temperatures enhances the
mechanical and electrical properties of the films. Films annealed at 410'C have a dielectric
constant of 2.15, hardness and modulus of 0.78 GPa and 5.4 GPa, respectively. These values are
comparatively better than previously reported results for CVD low-k films.
Environmentally friendly low-k processing encompasses materials and energy
management in the entire integration process, including lithography. Colloidal lithography was
combined with iCVD and capillary force lithography to create spatially addressable grafted
polymer pattern nanostructures, without the need for expensive lithography tools. Using this
method, we pattern our novel low dielectric constant polymer down to 25 nm without the need for
environmentally harmful solvents. Furthermore, these grafted patterns were produced for a broad
material set of functional organic, fluorinated, and silicon containing polymers.
A variation of this process created amine functionalized biocompatible conducting
polymer nanostructure patterns for biosensor applications. These were fabricated using grafting
reactions between oxidative chemical vapor deposition (oCVD) PEDOT conducting polymers
and amine functionalized polystyrene (PS) colloidal templates. Carboxylate containing oCVD
copolymer patterns were used to immobilized fluorescent dyes. Fluorescent colloidal particles
were assembled within dyed PEDOT-co-TAA copolymer nanobowl templates to create
bifunctional patterns for optical data storage applications.
Finally, UV and e-beam lithography were used to pattern covalently tethered vinyl
monolayers for resist-free patterning of iCVD and oCVD polymers, using environmentally
innocuous solvents.
Thesis Supervisor: Karen K. Gleason
Title: Professor of Chemical Engineering
To my wonderful parents, Jose and Velia Trujillo
AKNOWLEDGEMENTS
This page represents the proudest and most gratifying element of the thesis
process. Years of hard work and luck have helped bring together this thesis; however,
none of it would have been possible without the tremendous support from many
exceptional individuals.
Karen, you have been a phenomenal advisor and mentor. You have been
instrumental in helping me navigate through the whitespace of research and instilling in
me creativity in problem solving.
To my committee members, Professors Cohen and Love: your generosity,
expertise, and perspective have helped shape the direction of this thesis. Thank you.
My fellow Gleason group members have provided countless opportunities to
discuss and refine the various components of my research project. Many thanks go out to
Sung Gap, Sreeram, Sal, and Wyatt for showing me the tricks of the trade. Thank you to
Miles, Mahariah, and Jingling for being such great classmates, co-workers, and friends.
Thank you Gozde, Ayse, Rama, Rachel, Christy, and Hitesh for letting me bounce my
ideas off of you and for being generally great people. And to my fellow ChemE
classmates, "GO LANDAU!!!".
Thank you to all my friends back in California for believing in me. To my nonChemE friends at MIT, Kevin, Nareg, Nick and TJ: they say misery loves company, I am
glad that we have managed to keep each other out of her way. To my best friend Carly:
you are a blessing.
I would like to thank my undergraduate research advisor Professor Mike Sailor,
my brother-in-law Dr. Mike Hale, and my high school chemistry instructor Eric Gibson
for instilling in me a passion for chemistry. Dr. Jacqueline Azize-Brewer and the CAMP
research program have opened countless doors for me and greatly contributed to my
professional development. I wouldn't have reached MIT without their help.
My five siblings Christopher, Jonathan, Cesar, Cindy and Geraldine have always
been there whenever I needed them, in academics and in life. They rock!
Most importantly, I would like to thank my parents. Their limitless love and
support has ushered me through this challenging process. I am forever grateful.
TABLE OF CONTENTS
ABSTRA CT................................................................................................................-----.....----.2
3
DED ICA TION ...........................................................................................................................
4
A KN OWLED GEMEN TS.....................................................................................................
5
TABLE OF CON TEN TS.......................................................................................................
8
LIST OF FIGU RES ...................................................................................................................
LIST OF TA BLES...................................................................................................................14
15
CH APTER 1: INTROD UCTION .........................................................................................
16
1.1. Environm entally focused low -k m aterial processing..............................................
22
1.2. Environm entally focused low -k patterning............................................................
1.3. Grafting......................................................................................................................24
27
1.4. Patterning ...................................................................................................................
30
1.5. Scope of Thesis.......................................................................................................
1.6. References..................................................................................................................32
CHAPTER 2: ULTRA-LOW DIELECTRIC CONSTANT
TETRAVINYLTETRAMETHYLCYCLOTETRASILOXANE FILMS DEPOSITED BY
INITIATED CHEMICAL VAPOR DEPOSITION (ICVD)................................................37
2.1. Abstract......................................................................................................................38
2.2. Introduction................................................................................................................39
2.3. Experim ental..............................................................................................................42
44
2.4. Results and Discussion .........................................................................................
2.5. Conclusions................................................................................................................67
68
2.6. A cknow ledgem ents................................................................................................
69
2.7. Supporting Inform ation .........................................................................................
70
...........................
p(V4D4)
iCVD
for
Parameters
on
Deposition
Notes
2.8. Technical
74
2.9. Technical N otes on Porogen use w ith p(V 4D 4)..................................................
2.10. References................................................................................................................82
CHAPTER 3: MULTI-SCALE GRAFTED FUNCTIONAL POLYMERIC
NANOSTRUCTURES PATTERNED BOTTOM-UP BY COLLOIDAL
LITHOGRAPHY AND INITIATED CHEMICAL VAPOR DEPOSITION (ICVD)........86
3.1. Abstract......................................................................................................................87
3.2. Introduction................................................................................................................88
93
3.3. Experim ental Section............................................................................................
97
3.4. Results and D iscussion .........................................................................................
3.5. Conclusions..............................................................................................................115
3.6. Acknow ledgem ents..................................................................................................116
3.7. References................................................................................................................116
CHAPTER 4: OXIDATIVE CHEMICAL VAPOR DEPOSITION (OCVD) OF
PATTERNED AND FUNCTIONAL GRAFTED CONDUCTING POLYMER
NANOSTRUCTURES FOR ADVANCED BIOELECTRONIC APPLICATIONS............119
4.1. A bstract....................................................................................................................120
4.2. Introduction..............................................................................................................121
4.3. Experim ental............................................................................................................123
125
4.4. Results and D iscussion ............................................................................................
4.5. Conclusions..............................................................................................................133
4.6. Acknow ledgem ents..................................................................................................134
4.7. References................................................................................................................134
CHAPTER 5: MULTI-FUNCTIONAL TEMPLATE DIRECTED SELF-ASSEMBLY
TOWARDS HIGH DENSITY OPTICAL DATA STORAGE ............................................. 136
5.1. Abstract....................................................................................................................137
5.2. Introduction..............................................................................................................138
5.3. Experim ental............................................................................................................140
141
5.4. Results and Discussion ............................................................................................
5.5. Conclusions..............................................................................................................149
5.6. References................................................................................................................150
CHAPTER 6: UV AND E-BEAM PATTERNING OF VINYL COUPLING AGENTS:
TOWARDS RESIST-FREE PHOTOLITHOGRAPHY OF POLYMERIC THIN FILMS.. 152
6.1. Abstract....................................................................................................................153
6.2. Introduction..............................................................................................................154
6.3. Experim ental............................................................................................................156
158
6.4. Results and D iscussion ............................................................................................
6.5. Conclusions..............................................................................................................165
6.6. A cknow ledgem ents..................................................................................................165
6.7. References................................................................................................................166
CHAPTER 7: CONCLUSIONS AND FUTURE WORK.....................................................167
7.1. Conclusions..............................................................................................................168
7.2. U ltra-low D ielectric Constant Film s D eposited by iCVD ....................................... 168
7.3. Grafted Functional Polymeric Nanostructures by Colloidal Lithography...............169
7.4. Conducting Polymer Nanostructures for Advanced Bioelectronic Applications ....169
7.5. Multi-functional Template Directed Assembly Towards Optical Data Storage ..... 170
7.6. UV and E-Beam Patterning of Vinyl Coupling Agents for Polymer Patterning.....170
7.7. Future W ork.............................................................................................................170
APPENDIX A: INTEGRATIVE CAPSTONE PAPER: HLED TECHNOLOGIES ..... 173
175
EXECUTIVE SU MM A RY ...................................................................................................
178
The Team ........................................................................................................................
M ARKET AN A LY SIS..........................................................................................................180
M arket Segm entation......................................................................................................180
180
D isplay Sizes ...........................................................................................................
Industry....................................................................................................................182
Com peting Technologies.........................................................................................184
186
Competition and Com petitive A dvantage ......................................................................
A vionics/M ilitary A pplications...............................................................................186
187
M aterials D evelopm ent ...........................................................................................
Display Technology.................................................................................................188
188
G eneral Lighting A pplications ................................................................................
190
SALES & M A RKETING ......................................................................................................
190
Overall M arket Strategy .................................................................................................
Pricing.............................................................................................................................191
192
Sales Tactics ...................................................................................................................
6
Sales Force Growth.........................................................................................................192
193
Branding & Prom otion ...................................................................................................
194
TECHN OLOGY & PRODU CT OFFERING ........................................................................
194
Product Description ........................................................................................................
................................... 194
How does hLED technology work?.............................................
195
Intellectual Property Strategy .........................................................................................
Technical Risks...............................................................................................................195
196
D evelopm ent Resources .................................................................................................
Product Developm ent Tim eline and M ilestones.............................................................197
198
MANUFA CTURIN G , SERVICES, & LOGISTICS .............................................................
198
M anufacturing & D istribution ........................................................................................
198
Service ............................................................................................................................
Logistics..........................................................................................................................198
200
FINANCIALS & OW NERSH IP ...........................................................................................
Com pany Structuring......................................................................................................200
200
Financial Sum mary .........................................................................................................
Financial A ssumptions....................................................................................................202
206
Financial Projections ......................................................................................................
212
Breakeven Analysis ........................................................................................................
213
Financial Oversight and Cost Control ............................................................................
214
Exit Strategies .................................................................................................................
Ownership.......................................................................................................................214
Financial Conclusions.....................................................................................................216
216
A ddendum : Cap Chart ....................................................................................................
LIST OF FIGURES
17
Figure 1-1: Cross section and schematic of an integrated circuit. .......................................
Figure 1-2: Traditional (left-a) and (right-b) resistless lithography process flow .............. 24
Figure 2-1: FT-IR spectra for liquid V4D4 monomer and the as-deposited iCVD polymer,
p(V4D4). The gray bar highlights the position of the vinyl CH 2 absorption. The
reduction of this peak in the iCVD polymer is consistent with free-radical
polymerization, as is the formation of polyethylene-like backbones between 28782920 cm-1. The remaining vinyl groups are utilized as "built-in" porogens that are
removed in subsequent annealing. The lack of broadening in the Si-O-Si
stretching peak indicates that the cyclic siloxane D4 ring structure has been
47
p reserv ed ......................................................................................................................
Scheme 2-1: (a) Proposed initiation and propagation polymerization mechanism for the
iCVD p(V4D4). (b) Reaction stoichiometry required for two D4 rings to create a
substituted silsesquioxane cage structure through reaction with oxygen from the
48
amb ien t air. ..................................................................................................................
Figure 2-2: Thickness normalized FT-IR spectra for Si-O-Si stretching (al-a7) and Si-C
stretching (bl-b7), where the numbers 1-7 correspond to as-deposited p(V4D4)
and p(V4D4) annealed at 90'C, 170'C, 250'C, 330'C, 370'C, or 410'C,
respectively. The integrated peak areas for the various bonding environments in
(a) correspond to specific suboxide, network, or cage Si-O bonding, are plot as a
ratio of the total integrated Si-O peak area from 1000-1200 cm-I (c). The
primarily network structure evolves into primarily suboxide and cage structures as
51
the anneal temperature is increased. .......................................................................
Figure 2-3: Raman spectra of p(V4D4) films as-deposited and annealed at 410'C. The
preservation of the cyclic D4 structure is evident by the peak at 495 cm-1. The
peaks at 575 and 1117 cm-I that appear in the annealed structure correspond to
Si-O-Si stretching in organically substituted silsesquioxane cages. ..................... 53
Figure 2-4: Thickness normalized FT-IR for the Si-CH 3 bonding region for as deposited
p(V4D4) and films annealed at 90'C, 170'C, 250'C, 330'C, 370'C, or 410'C (ala7). Peaks at 1262 and 1272 cm-1 correspond to 'D' and 'T' groups, respectively.
The general trend demonstrates that the degree of silicon oxidation increases as
the anneal temperature is increased. The ratio of the integrated Si-CH 3 region
(1250-1280 cm- 1) to the total integrated Si-O peak area from 1000-1200 cm-I (b)
suggests the incorporation of 'Q' groups (fully oxidized silicon atoms).................56
Figure 2-5: Average film connectivity number plot versus anneal temperature (a). Films
annealed at temperatures below 330'C have connectivity below the percolation
threshold. The mechanical properties for the cured p(V4D4) (b) reflect drastically
increased hardness and modulus as the films approach a connectivity greater than
59
2 .4 .................................................................................................................................
Figure 2-6: Refractive index for various cured p(V4D4) films (a). The porosity (b) was
calculated using the Lorentz-Lorentz equation (2-1).............................................60
Figure 2-7: The dielectric constant is plot versus anneal temperature (a). The parabolic
shape is attributed to the evolution of highly polarizable carbonyl bonds, C=O.
The plot of the 17 10-1740 cm-I FT-IR spectral region (bl-b7) indicates that the
largest carbonyl incorporation occurs at an anneal temperature of 250'C (b4),
which corresponds to the highest dielectric constant. The dielectric constant
reflects that the reduction in film density is offset by the increased bond
63
p olarizab ility . ...............................................................................................................
Figure 2-8: A comparison between the best dielectric constant and modulus from this
study with previously reported results of merit for low-k OSG films. 9,51-54.....64
Figure 2-9: Proposed molecular model for the cured V4D4 films, which consist of MSQ
cages interconnected by crosslinking 'Q' groups....................................................65
Figure 2-10: The elemental ratios of carbon to silicon (a) and carbon to oxygen (b) plot
versus anneal temperature. The films lose a significant amount of carbon between
170'C and 250'C, as was suggested by the refractive index trend in Figure 2-6a......67
Figure 2-S1: TGA mass evolution for p(V4D4) films annealed under two different
annealing environments. The peaks in the bottom two traces correspond to the
respective temperatures for decomposition onset....................................................69
Figure 2-S2: Temperature evolution of various ions detected by residual gas analysis
70
(RGA). Helium was used as the purge gas. ............................................................
Figure 2-NI: Deposition rate data for polymer film growth as a function of substrate
temperature. The diamonds represent the deposition rate as measured in-situ by
interferometry and the open squares represent the film thickness measured ex-situ
72
by ellip som etry .............................................................................................................
Figure 2-N2: Deposition rate data for polymer film growth as a function of monomer
partial pressure as a fraction of saturation. The diamonds represent the deposition
rate as measured in-situ by interferometry and the open squares represent the film
73
thickness measured ex-situ by ellipsometry...........................................................
Figure 2-N3: FT-IR spectra for hybrid iCVD low-k copolymer films produced from
V4D4 precursors and CHMA (a)(b), IBMA (c), and Terpinene. The grey bar
highlights the position of the carbonyl peak between 1720-1740 cm-1. ................. 76
Figure 2-N4: Calculated porosity for p(V4D4-co-CHMA) hybrid films annealed in air at
77
various tem peratures. ..............................................................................................
Figure 2-N5: TGA mass decomposition profiles for as-deposited and hybrid V4D4 films
78
annealed in air or helium .........................................................................................
Figure 2-N6: Overall film shrinkage for various V4D4-co-CHMA copolymer films
annealed in air. The diamond and triangle series corresponds to CHMA:V4D4
79
ratios of 2:1 and 0.5:1, respectively .........................................................................
Figure 2-N7. Dielectric constant versus anneal temperature for various V4D4-co-CHMA
copolymer films annealed in air. The diamond and triangle series corresponds to
CHMA:V4D4 ratios of 2:1 and 0.5:1, respectively................................................80
Figure 2-N8: FT-IR spectra for iCVD low-k homopolymer (a) and copolymer films
annealed in air and produced from V4D4 precursors and CHMA (b), or IBMA
1
(c).................................................................................................................................8
Figure 2-N9: FT-IR spectra for iCVD low-k homopolymer (a) and copolymer films
produced from V4D4 precursors and CHMA (b), or IBMA (c)..............................81
Figure 3-1: Schematic of thin dot and ring patterns which form from 2-D colloidal
patterning of PECVD polymer (a). The dotted circles represent the colloid
template of radius 'r'. The polymer feature height, h, is typically much smaller
than 'r' (h << r). iCVD films can produce truly hemispherical "bowl" structures
from functional polymers. These structures can either be spaced apart (b) if the
film thickness is less than the particle radius (h < r) or directly neighboring (c) if h
1
~ r....................................................................................................................9
Scheme 3-1: A generic process scheme for creating a topographical template used for
producing hierarchical patterns of polymeric nanostructures, by capillary force
lithography. A patterned PDMS mold is pressed onto a polystyrene melt (alb).
After cooling, the mold is removed. A SAM of colloidal particles is deposited
into the grooves (c). This hierarchical template is used for patterning the iCVD
96
polym ers, according to Figure 3-1 ...........................................................................
Figure 3-2: A generic process scheme for producing patterned polymeric nanostructures
using colloidal lithography. A hydroxylated substrate which has been treated with
an oxygen plasma serves as a hydrophilic base for depositing a 2-D assembly of
colloidal nanoparticles (a). The masked sample is then treated with a vapor phase
silane coupling agent which covalently attaches vinyl groups to the substrate in
the exposed regions of the colloidal mask (b). This acts as an adhesion promoter
to graft the functional iCVD polymer which is subsequently deposited (c). The
grafted film is sonicated in solvent to remove the colloidal template and any
ungrafted polymer. This reveals an array of bowl-shaped nanostructures patterned
98
in a hexagonal arrangem ent (d)................................................................................
Figure 3-3: FT-IR spectra for (a) butyl acrylate monomer, (b) corresponding iCVD film,
(c) HEMA monomer, (d) corresponding iCVD film, (e) PFDA monomer, (f)
corresponding iCVD film, (g) PFM monomer, (h) corresponding iCVD film, (i)
V4D4 monomer, (j) corresponding iCVD film. The grey bar highlights the
position of the vinyl C=C absorption. The noted reduction in this peak in the
iCVD polymer is consistent with free-radical polymerization. The functional
similarity between monomers and their corresponding iCVD film is highlighted
with asterisks (*), and suggests the preservation of functional groups in the
2
polym er film s.............................................................................................................10
Figure 3-4: SEM images for grafted functional "nanobowls", produced from 1 pm
diameter spheres, after the colloid template had been removed. p(butyl acrylate)
patterns (a) were very well ordered . A large continuous pattern of pPFM (b) can
create a reactive surface. These patterns contain a reactive pentafluorophenyl ester
which was used to immobilize an amine-containing fluorescent ligand through
nucleophilic addition. The inset contains a fluorescence microscope image of the
fluorescent patterns. Hydrogel patterns from pHEMA (c) are incredibly
hydrophilic (inset) unlike those produced from low surface-energy pPFDA (d)
which are water repellent (inset). All iCVD films were devoid of wetting defects,
such as those which would have given rise to island type pattern growth. ............... 105
Figure 3-5: Typical AFM image and line scan for patterned "nanobowls" from 1 jim
diameter colloidal template, p(butyl acrylate) pictured. The tallest features are
about 500 nm in height. The line scan shows how the honeycomb polymer pattern
regularly preserves the hemispherical geometry from the colloidal template,
which is theoretically represented in the dotted white curve which appears as an
elliptical overlay on the graph since the horizontal and vertical scales are in ratio
107
of 4:1. The features traced are -300 nm in height. ....................................................
Figure 3-6: The grafted polymer patterns produced from 1 tm particles ( p(butyl acrylate)
shown) typically generate features 150 nm in width (a). Because of the vinyl
pretreatment these patterns are robust and withstand several hours in THF. The
silyation step is necessary to covalently attach the iCVD polymer to the substrate.
Without this step the polymer is easily washed away during the template lift-off,
leaving behind a clean substrate (b). The insets depict the corresponding substrate
functionality prior to patterning.................................................................................109
Figure 3-7: SEM images for patterned V4D4 dielectric polymer using (a) 1 tm, (b) 200
nm and (c) 80 nm diameter templates. The template was removed in an ultrasonic
bath of an environmentally-friendly solvent, isopropyl alcohol. The smallest
obtainable features were 25 nm in width, obtained from 80 nm particles.................111
Figure 3-8: Hierarchical patterns were preliminarily generated by micro contact printing
the colloidal template. AFM (a) and SEM (b) images of hierarchically patterned
V4D4 show high line-edge-roughness and stray beads within the unpatterned
113
reg io n . ........................................................................................................................
Figure 3-9: Hierarchical patterns from grafted iCVD polymer were produced with
capillary force lithography. A polystyrene template (a) was used to template the
colloidal assembly (b). The iCVD polymers (pHEMA shown) are patterned at two
length scales. The large length scale corresponds to the polystyrene template (c).
The smaller length scale is attributed to the colloidal template (d). .......................... 114
Scheme 4-1: PS beads are self-assembled on a vinyl-treated Si wafer to form a 2-D HCP
colloidal template (a). PEDOT is deposited via oCVD, conformally coating the
void space of the colloidal template with conducting polymer, which grafts to the
surfaces of the PS beads and the vinyl-treated wafer (b). The non-grafted cores of
the PS template are removed via dissolution and rigorous ultrasonication in THF,
revealing well-ordered PEDOT nanostructures with a grafted PS surface layer.......127
Figure 4-1: SEM images show a PEDOT shroud in which the internal PS template has
been dissolved away by brief ultrasonication in THF (a). Rigorous ultrasonication
reveals the hemispherical HCP geometry of the patterned PEDOT nanostructure
below (b). Using FeCl 3 as the oxidant yields a well-defined PEDOT/PS
nanostructure with a very smooth texture (c). When CuCl 2 is used as the oxidant,
hierarchically patterned PEDOT conducting polymer films are formed with
tunable nanoporosity (d). The inset captures the morphology of the porous
PED OT on an unpatterned substrate..........................................................................129
Figure 4-2: FT-IR spectra of a blanket oCVD PEDOT conducting polymer film (a), a 2-D
monolayer of 1 tm diameter polystyrene colloidal template (b), and oCVDpatterned conducting polymer nanostructures (c) in which the PS template was
removed by rigorous rinsing and ultrasonication in THF. The observation of PS
peaks in (c) is evidence of grafting between the PEDOT nanobowls and the
surface of the PS beads..............................................................................................130
Figure 4-3. Surface amine moieties provide a linkage point between the bulk conducting
polymer nanostructure and various ligands, demonstrated here by attachment of
NHS-tethered fluorescein (a). SEM image of oCVD PEDOT patterned using 1 pm
amino-functional PS beads (b); the inset captures the nanobowl shape, which
becomes evident at the interface with the unpatterned bulk PEDOT. Fluorescence
microscopy shows fluorescence areas patterned using amino-functional PS beads
(c); the inset shows the interface between the fluorescent patterned regions and
the unpatterned bulk PEDOT, which does not exhibit fluorescence after the
132
identical functionalization treatment (red arrow). .....................................................
Scheme 5-1: Carboxylic acid groups on patterned oCVD films (a) are directly reacted
with amine containing FITC dye (b) to create green patterns. Indirect reaction
with PDA and AMCA-NHS will create blue patterns (c and d). The dyed
nanobowls are then used for template directed assembly of fluorescent beads (e),
which creates bifunctional patterns............................................................................142
Figure 5-1: PEDOT homopolymer nanobowls containing statistically distributed
quantities of 200 nm diameter non-fluorescent polystyrene beads (p = 4.95 beads
143
per bow l, 5 = 2.13 beads per bow l). ..........................................................................
Figure 5-2: 500 nm diamter fluorescent orange polystyerene particles assembled within
PEDOT-co-TAA (functionalized with FITC-NH 2 dye) copolymer patterns
demonstrate two types of defects: two particles assembling within one bowl (a)
and particles attaching to the terrace of the nanobowl structure (b). 200 nm red
beads assembled within AMCA-NHS dyed PEDOT-co-TAA copolymer patterns
(c) (d) assemble in an analogous manner to the 200 nm diameter non-fluorescent
14 5
b ead s. .........................................................................................................................
Figure 5-3: Optical micrograph of 200 nm red beads assembled within AMCA-NHS
functionalized PEDOT-co-TAA nanobowls (a). When these patterns are
illuminated using a DAPI filter set, the two dyes become visible, demonstrating
bifunctional patterns (b). Image analysis decouples the dye signal corresponding
to the bowl perimeter(c) from the fluorescent bead signal (d). Fluorescence
micrograph for the template directed assembly of 1 prm diameter dyed beads onto
FITC-NH 2 functionalized PEDOT-co-TAA nanobowls (e). Trifunctional patterns
using two distinct fluorescent beads assembled atop FITC-NH 2 dyed nanobowls
148
resulted in an irregular assembly (f). .................................
Figure 6-1: Generic processing scheme for resist-free lithography. A vinyl silane treated
wafer (a) is exposed to deep UV light through a shadow mask (b). An iCVD
polymer blanket layer is deposited onto the irradiated substrate (c). The polymer
film covalently adheres to the unexposed regions of the substrate. Rinsing in a
solvent removes the untethered polymer layers and reveals patterned iCVD
p olym er (d).................................................................................................................156
Figure 6-2: FT-IR spectra for as-grafted TCVS monolayer on a silicon substrate (a) and
after 20 hours of photolysis with a UV lamp (b). The grey arrows indicate the
position of the photolyzed vinyl groups, which are present in the as-grafted film.
The reduced water contact angle reflects the removal of the organic monolayer
and the subsequent exposure of the underlying native oxide from the substrate.......159
Figure 6-3: 200 nm thick iCVD patterns were created from p(CHMA-co-EGDA) (a),
whereas only 20 nm thick patterns from iCVD p(butyl acrylate) remain after
liftoff in IPA (b). The use of a crosslinker can help generate thick patterns after
liftoff. Wetting contrast that is achieved after patterning grafted thin layers (<30
nm) of PEDOT via oCVD (c and d). The darker regions correspond to water
condensation on the UV exposed regions. PEDOT is located in the lighter regions. 161
Figure 6-4: Linewidth patterns ranging from 2 pm to 10 nm were written onto the vinyl
silane treated wafers by e-beam irradiation (a). iCVD was used to deposit a
blanket film of p(CHMA-co-EGDA) copolymers onto the pre-pattened substrates.
These films were subsequently rinsed in IPA. An optical micrograph (b) indicates
that polymer features smaller than 1 prm could not be resolved. ............................... 162
Figure 6-5: AFM image of 1 um p(CHMA-co-EGDA) linewidths developed from e-beam
pre-patterned substrates. The white line shows the region corresponding to the
accompanying line scan (bottom), which indicates an average height of the
patterned lines of 33 ± 3 nm with an average FWHM of 1.01 ± 0.01 pm......163
Figure 6-6: AFM images showing smaller polymer linewidths (<500 nm). For smaller
features, there is extensive line bridging which gives rise to features which look
like the capital letter 'H' (indicated by the white circle). .......................................... 164
LIST OF TABLES
Table 1-1: Typical values for bond polarizability and bond energy....................................19
20
Table 1-2: ITRS roadmap for interconnect technology ......................................................
21
Table 1-3: Material requirements for low-k integration ......................................................
Table 2-1: FT-IR peak assignments from the literature (v stretching, 6 bending, p ............ 46
rocking, to wagging, AS antisymmetric, and S symmetric)................................................46
Table 2-2: Raman shift assignments from the literature (v stretching, 6 bending, p
53
rocking, AS antisymmetric, and S symmetric)......................................................
Table 1-3: Atomic compositions calculated from XPS survey scans for various annealed
V4D4 films. The values corresponding to annealing at 4 10 C are within 1%of the
theoretical value for a film containing 83% 'T' groups and 17% 'Q' groups......66
70
Table 2-S1: Proposed fragments released during pyrolysis by TGA ..................................
74
Table 2-NI: Reactor conditions for deposition of iCVD p(V4D4) films ...........................
Table 2-N2: Summary of electrical, optical, and thermal performance for various as
deposited and annealed hybrid and homopolymer V4D4 films...............................82
Chapter 1
Introduction
1.1. Environmentally focused low-k material processing
The new millennium has brought fourth many technological innovations made
possible by the advancement of high speed digital electronics. At the heart of these
electronic devices are integrated circuits, whose performance has been improved by
shrinking transistor size in accordance to Moore's Law, which states that transistor
1
density on ULSI (ultra-large-scale-integrated) circuits doubles every 18 months. The
performance of these devices can be negatively affected by signal delays, cross talk
noise, and increased power consumption. The signal (RC) delay through the interconnect
system is given by:
=
OcpL2
(1-1)
0RC
m
TdTm
K = Dielectric Constant
p = Metal Density
Lm = Length of Metal Lead
Td = Thickness of Dielectric
Tm= Thickness of Metal Lead
To reduce the resistance for metal leads, R, copper metal (1.7 g -cm) has been
substituted for the traditional aluminum (3.0 tQ-cm) interconnect. 2Increasing transistor
density means smaller inter-metal
dielectric
(IMD) features,
which require
a
corresponding decrease in dielectric constant in order to keep capacitance, C, low.
Reduced capacitance will also decrease the power consumption, P, and cross talk noise,
N,
:-... ::M
:M
:-: :M
:: ::.:::::
...............
- ..............
--- .
.
.
...........
...............
P - CV2f
(1-2)
f = Frequency of Operation
N
(1-3)
~ Cetoline_
C total
thus boosting device performance. Indeed, at the current transistor length scale of 65 nm,
performance limitations result from interconnect delay rather than intrinsic gate delay. 2
Therefore, reducing IMD dielectric constant becomes an important parameter for
improving device performance. Figure 1-1 depicts a cross section and schematic for an
integrated circuit.
Metal
T.
Dielectric
Td
Figure 1-1: Cross section and schematic of an integrated circuit.
There are two main aspects of material design that affect the dielectric constant:
material polarizability and density. The polarizability, P, measures the electronic, atomic,
and orientation response of a material to an applied electric field, E.3 At device operating
frequencies this relates to the dielectric constant, k, through:
k =1+
E
(1-4)
The atomic and orientation contributions to polarization are nuclear effects, and become
important at low device frequencies. At higher frequencies (>1013 Hz) the electronic
polarization dominates, and the dielectric constant can be approximated as the square of
the optical refractive index, k=n2 . Typical devices operating frequencies are < 109 Hz,
thus all three components of polarization contribute to the dielectric constant. 3
Nuclear polarization typically arises from permanent and transition dipoles in a
material. Polar substituents such as hydroxyl and carbonyl groups would likely contribute
to these dipoles and may attract water. The large permanent dipole in water raises the
orientational contribution to polarization, thus careful consideration must be taken in
material design to avoid polar substiuents which adsorb moisture.3-5
Electronic polarization measures the induced dipole moment per unit volume for
particular bonding environments. Table 1-1 shows typical values for bond polarizability6
and associated bond enthalpy. Highly electronegative bonds have electrons tightly bound
to the nucleus-less likely to be displaced by an electric field-
and have the lowest
electronic polarizability. Conversely, conjugated bonding environments, such as carbon
double bonds and aromatic rings, demonstrate delocalization of i electrons and result in
high polarizability. However, there is a tradeoff: low polarizability bonds are usually
weaker.
Table 1-1: Typical values for bond polarizability and bond energy
Polarizability Bond Energy
Bond
(A3)
Kcal/mol
C-C
C-F
C-0
C-H
0-H
C=O
C=C
C=C
C=N
0.531
0.555
0.584
0.652
0.706
1.020
1.643
2.036
2.239
83
116
84
99
102
176
146
200
213
Organosilicon polymers are a class of low-k materials identified to facilitate
integration into interconnect structure.! These materials, also known as carbon-doped
silicon oxides, or organosilicon glasses (OSG's), contain Si:O:C:H bonding structures
which lowers the average bond polarizability when compared to silicon dioxide, k=3.9.
This class of materials have also demonstrated superior thermal stabilityl when compared
to materials with lower polarizability, such as C:F films7 or fluorinated silicon glasses
(FSG).1''',
Other methods for reducing the dielectric constant are to reduce the film density
by incorporating void space and using precursors with inherently open structures. Void
space can be induced by copolymerization of the low-k matrix with a thermally sensitive
porogen molecule, which is removed in a post-processing anneal. The void space
contains air, k=1 (the theoretical lower limit for k), which lowers the effective density of
the film. The Bruggemann, 9 Rayleigh,' 0 and Looyenga" models model porosity and can
predict the effective dielectric constant for heterogeneous films. In contrast to tunable
porosity obtained through use of porogens, intrinsic porosity can be achieved through the
polymerization of cyclic precursors into cage type Si-O structures.1214 These structures
......
............................................................
....................................................................................
.......................
.. ....
..................
--__
------____-
contain molecular nanoporosity which can be persevered through deposition and lower
the film density and dielectric constant.
The ITRS is a fifteen-year assessment of the semiconductor industry's future
technology requirements. These needs drive present-day strategies for world-wide
research and development among manufacturers' research facilities, universities, and
national labs. The 2006 ITRS roadmap for interconnect,' 5 Table 2-2, has been updated to
accommodate integration and characterization challenges for new low-k materials, which
now sets the goal for the 36 nm node at a dielectric constant of 2.1. 2008 was the first
year that specific EHS technology requirements existed. Therefore the IMD research
thrust must shift to incorporate the materials management requirements for EHS friendly
processing. By 2011 this requires 90% raw chemical utilization in IMD processing. This
suggests modifications to the current IMD processing to reduce the solvent waste streams
and to avoid spin-on processes, which are wasteful.16-18
Table 1-2: ITRS roadmap for interconnect technology
Year
2001
2003
2004
2007
2010
2013
2017
Technology
130
130
90
65
45
32
20
3.0-3.6
2.6-3.1
3.3-3.6
3.1-3.6
Node (nm)________
2001
Rodmp3.0-3.6
Roadm
2.7-3.0
.
:24
Roadmap
2006
Roadmap
Updated 2006
Roadmap
2.3-2.7
5
S.
2.1-2.4
EHS for CVD
and Spin-On Minimum emissionslwaste processes
Manufacturable
Solutions Known
T522:2 ;WKM
...
....
There are several key considerations when designing low-k materials, other than
dielectric constant. In order to integrate a low-k material into an interconnect structure,
the multiple criterion in Table 2-3 must be satisfied simultaneously.1, 2 Whereas historical
consideration for good dielectric materials were primarily concerned with attractive
electrical, chemical , mechanical, and thermal properties, new dielectric processing must
be concerned with new EHS focused roadmap requirements. Therefore, the paradigm in
IMD materials selection must shift to include only materials which can be processed in an
environmentally friendly manner.
Initiated chemical vapor deposition (iCVD) is a variation of hot filament chemical
vapor deposition and is a one-step, solvent-free process, requires an order of magnitude
lower energy density for film deposition when compared to PECVD.' 9 The all vaporphase process avoids the material waste associated with spin-on processing. This thesis
introduces iCVD as an environmentally focused process that is capable of producing lowk films with attractive mechanical and electrical properties.
Table 1-3: Material requirements for low-k integration
Electrical
low K
low dissipation
low leakage
low charge trap
high breakdown
high resistivity
Mechanical
film uniformity
adhesion
low stress
high tensile modulus
low shrinkage
high hardness
elasticity
Chemical
low moisture absorption
high etch selectivity
high chemical resistance
high purity
no metal corrosion
low gas permeability
Thermal
high thermal stability
high glass transition
high thermal conductivity
low thermal shrinkage
low thermal expansion
1.2. Environmentally focused low-k patterning
Environmentally friendly low-k processing encompasses materials and energy
management in the entire integration process, including lithography. The schematic on
the left in Figure 1-2 represents the process flow for conventional photolithography. To
define the lithography pattern a photoresist material must be deposited onto the dielectric
film, irradiated with UV light, and developed in an aqueous base. The low-k material is
patterned by a subsequent plasma etch.2 Typical semiconductor foundries use 25,000
liters of photoresist materials annually, at a cost of
-$1,600
per liter. In spin-on photo
resist processing -95% of resist is wasted and disposed as toxic material.18 Furthermore,
the total weight of secondary fossil fuel and chemical inputs to produce a single 2-gram
32MB DRAM chip are estimated at 1600 g and 72 g, respectively.
1
Therefore, there are
opportunities for reducing the materials and energy requirements by simplifying the
process flow for lithography.
The schematic on the right in Figure 1-2 represents a proposed scheme for
resistless patterning using a form of non-conventional lithography. In contrast to
conventional lithography, patterning occurs before dielectric deposition. A monolayer of
a grafting agent, adhesion promoter, is deposited onto a silicon substrate by a vapor
deposition process. A pattern is created on the monolayer by e-beam irradiation, exposure
to deep UV radiation, or with a 2-D assembly of colloidal nanoparticles. A blanket of
low-k material is subsequently deposited by iCVD. The unexposed areas of the
monolayer retains vinyl functionality which can covalently link the iCVD polymer.
Because of the high adhesion contrast, the exposed (patterned) regions, which contain no
vinyl, can be recovered by removing the non-tethered polymer with an environmentally
friendly solvent such as IPA. A common positive tone resist developer, tetramethyl
ammonium hydroxide, poses health hazards when handled22 and acute aquatic toxicity
testing of a neutralized solution has shown it to be highly toxic to organisms. On the
other hand, IPA is biodegradable, not likely to bioconcentrate, and has low potential to
affect organisms. Moreover, no plasma etch is required to resolve features. This
eliminates a >7.5W/cm2 power requirement2o and preserves organic moieties23,24 which
help keep k low in porous dielectrics. The resist-free patterning of low-k materials
through non-conventional lithography is an off-roadmap approach to process-step
reduction. Successful implementation, in combination with a compatible iCVD dielectric,
represents a significant EHS and economic win-win.
The successful implementation of an EHS compatible, low-energy process for
creating well-defined nanostructures from low-k materials requires the integration of two
distinct, but complimentary, processes; grafting and patterning. The following sections
provide an overview of grafting and patterning strategies that have been successful in
creating well defined, robust nanostructures from a variety of functional CVD polymers.
These principles serve as a basis for the development of the novel patterning techniques
described in this thesis, which, by design, are amenable to various polymers produced by
iCVD and oxidative chemical vapor deposition (oCVD). 25
....
............................................
........
......
....................................
....
....
..
..........
...........................
Conventional
Lithography
d
spin-on4&
imaging layer
. ...................
..........................
Non-conventional,
VS.
Resistless
Lithography
CYD of grafting agent
itetric1.
m
'Wet chemistryeliminated
selective
2. rm5tles/E-beam
irradiation
lithography
development in
0
aqueous base
chemistryeliminated
3. iCVD dic
dielectric
patterning
4. Liftoff in I
imaging
prFiplfy
9cssig
Reduce ESH
impac
Figure 1-2: Traditional (left-a) and (right-b) resistless lithography process flow
1.3. Grafting
Control over interfacial adhesion is particularly important when integrating
materials of choice with device design. Although conformal vapor deposition processes
can be used to impart well-defined surface functionality to substrates with complex
surface geometries, the mechanical and chemical stability (overall "robustness") of this
26
coating is dictated by the molecular interaction between the coating and the substrate.
The hydrophobic nature of many functional polymer coatings often means that there is
inherently poor interfacial adhesion to polar substrates. Poor interfacial adhesion is a
limiting step in patterning dense sub-micron organic electronic features and can lead to
cracks, delamination, and displacements. 2,8Incidentally, many functional polymers
either swell or dissolve in common solvents such as THF, toluene, and chloroform, thus
demonstrating poor chemical stability. They can be rendered insoluble by introducing
covalent interaction between the polymer coatings and the substrates with a procedure
known as grafting. In order to remove the grafted polymers from the substrate, covalent
bonds must be broken. Thus, grafting also provides some measure of abrasion resistance.
Properly engineering the substrate/coating interface allows an additional degree of
freedom for designing robust devices and affords the ability to deposit functional CVD
polymers for a specific application, regardless of the substrate.
Procedures for increasing the interfacial adhesion between functional CVD
coatings and substrates are adopted from the widely used "grafting to" and "grafting
from" principles in solution phase chemistry.
29
A common approach for grafting
polymers deposited from the vapor phase requires chemical activation of the substrates.
Organic or inorganic substrates can be chemically activated prior to polymerization by
creating reactive free radical species on the surface. Rainby and coworkers used near UV
irradiation (> 300 nm) coupled with a type 11 photoinitator, benzophenone, to create
reactive sites on polyethylene and polystyrene substrates for graft polymerization of
vapor deposited polyacrylic acid. 30 The UV activated photoinitator forms an excited
triplet state, which can abstract a hydrogen atom from the substrate to initiate
polymerization. 26 Similarly, Albertson and co-workers used wide range UV irradiation
(270-420 nm) and vapor phase monomer precursors for covalently coupling acrylamide
to poly methylmethacrylate substrates. 31 The immobilized acrylamide was then converted
into a primary amine by a Hoffmann reaction, which was useful for bio-coupling
reactions. This UV grafting procedure was also used for vapor phase grafting of maleic
anhydride onto poly ethylene terephthalate substrates for protein coupling applications.
32
Using grafting chemical vapor deposition (gCVD), our group has demonstrated a low
temperature UV grafting process for covalently tethering antimicrobial dimethylamino
methyl styrene (DMAMS) polymers to nylon fabric.33
Organic substrates can also be chemically activated using a plasma glow
discharge.34'35 This activation generates free radical species on the substrate that can
initiate polymerization when contacted with gas phase polymer precursors. This
technique has been used to initiate vapor phase graft polymerization of HEMA on cotton
fibers 36 and vinyl pyridine vapors on polyamide substrates. 37 Precise control over the
plasma parameters is essential to prevent substrate etching from becoming the dominant
process in the modification of the material surface. 34 Extensive work on plasma activated
grafting has recently been reviewed by Griesser and coworkers.38
Alternatively, inorganic substrates can be chemically activated using a piranha
solution39 or oxygen plasma pretreatment*0 to create a high density of surface hydroxyl
groups. These surface hydroxyl groups readily hydrolize silane coupling agents to
covalently tether adhesion promoters41 or surface initiators for graft polymerization.29 For
example, various types of initiators have been immobilized with the use of silane
coupling agents. The coupling agent (3-aminopropyl)trimethoxysilane has been used to
immobilize
an azo free-radical photo initiator for photo-induced vapor phase
polymerization of vinyl monomers.42 The methodology originally developed by Chang
and Frank for surface-initiated vapor deposition polymerization (SI-VDP), covalently
couples (3-aminopropyl)-triethoxysilane (APS) to hydroxylated substrates.4 3 APS can be
used to initiate grafting polymerization for homo and block co-polypeptides from Ncarboxy anhydride peptide precursors. 44 Similarly, the coupled silane initiator 1-(4'-oxa2'-phenyl-12'-trimethoxysilyldodecyloxy)-2,2,6,6-tetra-methylpiperidine
("TEMPO")
was thermally activated and used for polymerizing various grafted homo and block
copolymer brushes via nitroxide-mediated free radical polymerization. 4 5
Since the total quantity of initiating species is fixed when using surface tethered
initiators, this fundamentally limits the overall growth rates and thickness of the grafted
films. Grafted silane adhesion promoters can avoid these issues by immobilizing passive
chemical groups that become integrated into the growing polymer backbone. Because
thes'e groups do not dictate the polymer reactivity, initiators can be continuously supplied
throughout the polymerization to encourage high growth rates and grafted thickness.
Trichlorovinylsilane coupling agents impart dangling vinyl groups onto silicon substrates.
These groups are indistinguishable from those belonging to vinyl monomers and have
been used to create grafted polymer layers from various iCVD precursors.19 The vinyl
groups on stainless steel stents treated with a vinyl-triexthoxysilane adhesion promoter
(A-174) immobilized vapor deposited poly-p-xylyelene for drug release applications.
We have shown tremendous adhesion
46
enhancement for oCVD PEDOT
conducting polymer films deposited onto silicon substrates treated with phenoltrichlorosilane.
The aromatic phenol groups act grafting sites when exposed to the
Friedel-Crafts catalyst, which is used as the oxidizing agent. Thus, this technique also
allows for linker-free grafting of oCVD conducting polymers onto flexible substrates
containing aromatic rings, which is desirable for advanced organic microelectronics
applications. Furthermore, these grafting techniques can prevent delamination at the
edges of high resolution patterned features.
1.4. Patterning
The high molecular weight and suppressed lateral diffusion of polymer films have
made them a popular target for novel patterning applications. 4 7 High-resolution
functional polymer patterns have recently gained exposure from their wide spread
applications
in
tissue
engineering
and
bio-sensors, 48-51
anti-biofouling, 52,53
microelectronics,54-56 optics,47,57 and MEMS.58 Vapor deposited polymer films can be
used to create topological and chemical patterns as well as their combination.
Both conventional59-63
or non-conventional
lithography42,60,64 can produce
topology in functional CVD polymers. These relief structures can serve as a resist to
enable patterning of an underlying layer or to subsequently immobilize specific target
molecules or nanoparticles.65-67 Traditional subtractive processing of polymers is often
incompatible with functional group retention. The use of high energy plasma etching or
corrosive solvents in pattern transfer from the resist to the organic CVD underlayer can
destroy the delicate reactive moieties in the CVD films. 68,69 These issues are exacerbated
by the lack of etch selectivity between organic CVD layers and organic resists.70 Additive
processing can eliminate some of these difficulties; however, the pattern resolution and
achievable film thicknesses can be limiting.
71
Another approach is to chemically pattern blanket film of the vapor deposited
polymer by selectively localizing target molecules onto the reactive films using an
elastomeric stamp,
72-74
-
77,78
75,76
A
or other spatially selective transfer process.7,
hard mask,
combination of topological and chemical patterning have been extensively used for
selectively immobilizing biomolecules onto vapor deposited patterns from functionalized
79
poly-xylylene films. ~87
CMOS processing offers the ability to create high resolution patterns from CVD
polymers and is the most promising method to accommodate in vivo measurements using
systems-on-chip.88 HWCVD (including iCVD) 89-91 and PVD92 have been used to deposit
"dry" positive and negative tone e-beam resists that are compatible with supercritical CO 2
development. These resists overcome the shortcomings associated with patterning using
traditional solution deposited polymer photoresists
89,92
and lateral resolution as small as
300 nm have been achieved. The conformal nature of CVD allows application of resist
90,93
layers onto non-planar substrates. ' Furthermore, eliminating "wet processing" prevents
pattern collapse of high aspect ratio features during drying, 94 avoids solvent residues and
impurities, 92,94 and reduces the negative environmental impact associated with large
volumes of solvent. 90
High resolution e-beam patterning was achieved on grafted oCVD and functional
iCVD layers. 95,96 Poly(propargyl methacrylate) (PPMA) is a click-active iCVD polymer
that exhibits direct positive tone sensitivity to e-beam irradiation. PPMA was directly
patterned down at 200 nm resolution without a resist.96 Grafting provides these films with
the chemical and mechanical stability necessary for withstanding subsequent click
functionalization with selectively conjugated quantum dots. Furthermore, oCVD PEDOT
was successfully grafted onto a flexible PET substrate and e-beam patterned to create
robust, well-defined 60 nm lines. 95
Materials patterning through non-conventional lithography can reduce the cost of
patterning fine structures when compared to traditional nanofabrication techniques.60
Capillary force lithography (CLF) 97 has been used for creating 110 nm line patterns from
bifunctional CVD polymers for one pot self-sorting bio-functionalizable surfaces.9 8 TEM
grids have been used as templates for patterning high-fidelity micrometer-scale patterns
of alternating hydrophobic and hydrophilic materials deposited by PPCVD 99 and as a
shadow mask for styrene graft polymerization from maleic anhydride pulsed plasma
polymer
films.100 Microcontact
printing has been
used to selectively deposit
photoinitiators for additively patterned piCVD polymer films. 7 1
Vapor deposition can produce inherently nano-structured polymeric materials.
10
Oblique angle deposition can generate columnar 1 or helicalio2 nanowire assemblies
from poly-xylylene films. These structures can support fibroblast cell attachment,o 3 have
tunable wetability,104 and can be electro-less templated with metals
02
for catalysis and
SERS applications.105 HFPO fluorocarbon films with inherent nano and micro-structure
have been deposited using HWCVD.' 0 6-io8 Basalt-like surface Morphology was generated
in oCVD films by introducing CuCl 2 as the oxidant.109 The pore size and porosity for the
conducting polymer films could be systematically tuned by modulating the substrate
temperature.
1.5. Scope of Thesis
Chapters two through six are structured as journal articles, each containing
independent introduction, experimental methods, results and discussion, and chapter
conclusions. Although each chapter can be read as independent work, there is clear
connection between chapters four through six with the novel underlying methods and
motivations described in chapters two and three.
Chapter two presents the synthesis and characterization of a novel low-k polymer
thin film, p(V4D4), deposited by initiated chemical vapor deposition. Simultaneous
reduction in the dielectric constant and improvement in the mechanical properties are
achieved when these films are thermally cured in air. The solvent-less and low-energy
nature of iCVD make it attractive from an environmental safety and health perspective
when compared with traditional methods for low-k material synthesis. This chapter also
contains technical notes for p(V4D4) deposition conditions and describes the properties
of p(V4D4) copolymer films produced from a variety of porogen precursors.
Chapter three details a novel technique for creating grafted multi-scale patterns of
functional iCVD polymers by colloidal lithography. These grafted "nanobowl" patterns
are produced for a broad material set of functional organic, fluorinated, and silicon
containing polymers Using this method, we patterned p(V4D4) down to 25 nm without
the need for environmentally harmful solvents. By combining this process with capillary
force lithography, we created spatially addressable topographical templates for largescale orientation of the grafted nanostructures.
Chapter four extends the principles developed in chapter three to conducting
polymer thin films produced by oxidative chemical vapor deposition (oCVD). We present
a simple one-step process to simultaneously create patterned and amine functionalized
biocompatible conducting polymer nanostructures. The surface functionality affords the
ability to couple bioactive molecules or sensing elements for various bioelectronic
applications.
Chapter five demonstrates a process for creating multifunctional hierarchical
nanostructures from the patterns described in chapter four. These types of materials are of
interest for high density optical data storage. Bi-functional patterns are created by
assembling commercially available dyed polystyrene beads within functionalized
nanobowls produced from reactive oCVD copolymers. A method for producing trifunctional structures is proposed.
Chapter six introduces the concept of resist-free photolithography; macroscopic
iCVD and oCVD polymer pattern definition by lithography at the monolayer level.
Because only a monolayer needs to be irradiated, this technique theoretically requires
much less energy density when compared to traditional photoresist irradiation and
precludes the use of expensive and toxic photoresists.
Chapter seven contains the conclusions for the previous sections and discusses the
directions for future work.
The funding for chapters two three and six was provided by NSF/SRC
Engineering Research Center for Environmentally Benign Semiconductor Manufacturing.
The work reported in chapters four and five was supported in part by the US Army
through the Institute for Soldier Nanotechnologies, under Contract DAAD-19-02-0002
with the US Army Research Office. This work made use of the shared electron
microscopy facility in the MIT Center for Materials Science and Engineering (CMSE);
the MRSEC Shared Experimental Facilities supported by the National Science
Foundation under award number DMR - 0819762; and the XPS facility at the Cornell
Center for Materials Research (CCMR) with support from the National Science
Foundation Materials Research Science and Engineering Centers (MRSEC) program
(DMR - 0520404).
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Chapter 2
Ultra-low dielectric constant
tetravinyltetramethylcyclotetrasiloxane films
deposited by initiated chemical vapor
deposition (iCVD)*
Nathan J.Trujillo, Qingguo Wu and Karen K. Gleason
*Published in Advanced Functional Materials (2010) 20, 607- 616
2.1. Abstract
Simultaneous improvement of mechanical properties and lowering of the
dielectric
constant
occur
when
films
grown
from
the
cyclic
monomer
tetravinyltetramethylcyclotetrasiloxane (V4D4) via initiated Chemical Vapor Deposition
(iCVD) are thermally cured in air. Clear signatures from silsequioxane cage structures in
the annealed films appear in the Fourier transform infrared (1140 cm 1 ) and Raman (1117
gm 1 ) spectra. The iCVD method consumes an order of magnitude lower power density
than the traditional Plasma Enhanced Chemical Vapor Deposition, thus preserving
precursor's delicate ring structure and organic substituents in the as-deposited films. The
high degree of structural retention in the as-deposited film allows for the beneficial
formation of intrinsically porous silsequioxane cages upon annealing in air. Complete
oxidation of the silicon creates 'Q' groups, which impart greater hardness and modulus to
the films by increasing the average connectivity number of the film matrix beyond the
percolation of rigidity. The removal of labile hydrocarbon moieties allows for the
oxidation of the as-deposited film while simultaneously inducing porosity. This
combination of events avoids the typical trade-off between improved mechanical
properties and higher dielectric constants. Films annealed at 410'C have a dielectric
constant of 2.15, hardness and modulus of 0.78 GPa and 5.4 GPa, respectively. The
solvent-less and low-energy nature of iCVD make it attractive from an environmental
safety and health perspective.
2.2. Introduction
The new millennium has brought fourth many technological innovations made
possible by the advancement of high speed integrated circuits. As the average feature size
in integrated circuits continues to decrease according to Moore's Law, reducing the
dielectric constant (k) of the interconnect dielectric (ILD) becomes crucial to minimizing
RC delay, power consumption and cross talk noise.' The International Technology
Roadmap for Semiconductors (ITRS) requires ILD with bulk dielectric constants between
2.1-2.5 by the 32 nm technology node (2012). The materials and energy requirements for
an integrated circuit is orders of magnitude higher than that of "traditional" goods, which
is due to its extremely low entropy, organized structure. 2 Thus, the ITRS has also set
fourth materials management requirements for environmental health and safety (EHS)
friendly processing to increase raw materials utilization in low-k processing by 10% each
year.3 The difficulty in reconciling technological challenges with the environmental
requirements for low- k processing is quite clear. The ITRS EHS milestones used to be
more ambitious and had to be modified; as recent as 2006, the roadmap set a 90%
materials utilization goal for 2011.4 Whereas historical consideration for good dielectric
materials were primarily concerned with attractive electrical, chemical, mechanical, and
thermal properties, new dielectric processing must be concerned with new EHS focused
roadmap requirements. Therefore, the paradigm in ILD materials selection must shift to
include only materials which can be processed in an environmentally friendly manner.
Organosilicon polymers are a class of low-k materials identified to facilitate
integration into interconnect structure.5 The stringent criterion for low-k integration has
led to much experimentation with novel organosilicate glass (OSG) precursors. Various
strategies have been identified for depositing low-k films from organosilicon precursors.
Silesesqioxane (SQ) precursors are popular among low-k researchers for spin-on
materials because of the open structure and high intrinsic porosity, which are
advantageous characteristics for low-k films. 6,7 Silsesquioxane cages contain a large
degree of constitutive porosity, which is owed in part to the large free volume of the cage
structure and organically substituted silicon atoms. Their dielectric constants are typically
very low compared to dense oxides,' however, their spin-on deposition techniques
require large volumes solvents, which is incompatible with the stringent EHS materials
management requirements. 8
PECVD materials are favored in facilitating integration into interconnect
structures, and generally have better mechanical properties than spin-on materials. For
example, PECVD of OSGs has been demonstrated to facilitate three-dimensional
crosslinking reactions by addition of an oxidant feed gas.5 '9 Several cyclic siloxane
precursors have been studied by PECVD. Most studies have been limited to
cyclosiloxane structures with more than three siloxane units (D3), as their ring structure
is non-planar and unstrained.10 Dense films produced from tetramethylcylotetrasiloxane
(H4D4),'"
octamethylcyclotetrasiloxane
(OMCTSO),"
and
decamethylcyclopentasiloxane (DMCPSO), 13 have been created with dielectric constants
of 2.4, 2.8, 2.7 respectively.
Although PECVD is a workhorse for the semiconductor industry, it is also a high
energy process that can destroy organic moieties through unwanted side reactions.1 The
retention of these organic functionalities have been associated with a lower dielectric
constants in dense PECVD films." iCVD is a variation of hot filament chemical vapor
deposition and is a one-step, solvent-free process that requires an order of magnitude
lower energy density for film deposition when compared to PECVD.15 Unlike PECVD
mechanisms that deposit films with various bonding environments, iCVD chemistry is
well understood and most closely resembles free-radical polymerization in solution.
In contrast to the real-time oxidation driven deposition mechanisms in PECVD
films, the well-defined free-radical polymerization chemistry of the iCVD process allows
us to systematically tune the film composition through post process thermal oxidation and
removal of unstable organic moieties. The precursor selected for the current work is
1,3,5,7-tetravinyltetramethylcylclotetrasiloxane
(V4D4). This precursor is an eight-
member cyclic siloxane ring with an analogous structure to commercially used low-k
PECVD precursors such as TOMCATs® (tetramethylcyclotetrasiloxane). The four vinyl
groups have two roles. First, they are necessary for the free-radical polymerization by
iCVD. The iCVD process acts to "loosely" bind the precursors through a 3-D network of
polyethylene-like backbones that emerge from these vinyl groups. Second, since the
organic content and precursor structure is preserved through the deposition, the
systematic substitution and eventual elimination of these groups by oxygen incorporation,
simultaneously improves mechanical properties while reducing the dielectric constant.
Furthermore, we have previously demonstrated that iCVD polymerized V4D4
films can be patterned to 25 nm feature sizes using environmentally focused patterning
techniques.
Therefore, because iCVD is an all dry, low-energy input process that is
compatible with environmentally focused patterning, its integration into BEOL low-k
processing can represent an economic and environmental win-win. The purpose of this
report is to demonstrate that the post processing of a novel iCVD polymer film, p(V4D4),
creates a well-defined, environmentally friendly material, that is promising for low-k
processing.
2.3. Experimental
The custom built iCVD vacuum reactor configuration has previously been
detailed.16 V4D4 (Gelest, 98%) monomer heated to 110*C, and tertbutyl peroxide
(Aldrich, 98%) initiator, at room temperature, were delivered into the reactor at 1.0 sccm
and 0.5 sccm, respectively. The initiator and monomer flow rates were regulated with
needle valves. Films were deposited on low resistivity (<1 ohm-cm), 100 mm diameter
silicon wafers (Wafer World Inc.). The reactor pressure, substrate temperature, and
filament temperature were maintained at 350 mTorr, 55*C, and 300"C, respectively. The
deposition rate was monitored in real time with a He-Ne laser (JDS Uniphase)
interferometer system.' 6
As deposited samples were annealed in atmospheric ambient for 1 hour using a
Barnstead SP 131325 hot plate. The hot plate surface temperatures were calibrated using
a 100 mm thermocouple silicon wafer (Thermodynamic Sensors) containing an assembly
of 17 thermocouples. Samples were annealed at 90 0C, 170 *C, 250 "C, 330 "C, 370 *C, or
410 "C.
The iCVD film composition was elucidated by transmission mode FT-IR
spectroscopy (Nicolet Nexus 870 ESP) using a DTGS-KBr detector. Spectra were
obtained through the samples over the range of 400 cm-i 4000 cm 1 at 4 cm-1 resolution
averaged over 64 scans, and baseline corrected. The sample chamber was purged with
dry nitrogen for 10 minutes prior to acquiring spectra. The background was taken from an
uncoated silicon wafer that was subsequently coated with iCVD polymer. All spectra
were
thickness
normalized
for qualitative
and quantitative
comparison.
Peak
deconvolution and area calculations were performed using the Gaussian peak fitting tool
in OMNIC software.
Resonant Raman spectra were obtained using a Kaiser Optical Systems Inc.
Hololab 500OR Modular-Research Micro-Raman Spectrograph with 514.5 nm laser line
excitation, through a single mode fiber, and 5.5 mW power at the sampling stage under
50 times magnification. V4D4 films were scraped from the silicon substrate with a clean
razorblade and pressed with a stainless steel pellet onto gold coated glass slides.
Collection time varied from 10 seconds to 30 seconds per sample, depending on the time
required to achieve 80 percent saturation at the CCD detector.
X-ray Photoelectron Spectroscopy (XPS) survey scans were performed using a
Science Instruments
Surface
SSX-100
with operating pressure < 2x10~9 Torr.
Monochromatic AlK-alpha x-rays (1486.6 eV) with a 1000 micron beam diameter were
used. An electron flood gun was used for charge neutralization. Photoelectrons were
collected
at a 55 degree emission angle. A hemispherical analyzer
collected
photoemission electrons, with a pass energy of 150V for the survey scans. The energies
analyzed correspond to the Is level in carbon (284 eV) and oxygen (532 eV) and the 2s
level in silicon (153 eV). Atomic concentrations were determined using the Scofield
relative sensitivity factors in CASA software, corrected using the methods of Ward and
Wood.17
Film thicknesses and refractive indices were measured using a J.A. Woollam M2000S spectroscopic ellipsometer equipped with a xenon light source. Data was collected
at 68' incidence angle for 190 wavelengths between 315nm and 718 nm. The data was fit
to a Cauchy-Urbach model1 8 from which the thickness values and optical parameters
were extracted. Refractive index values are reported at a wavelength of 633 nm.
The dielectric constant was determined from electrical measurements performed
with a mercury probe instrument from MDC. For each sample, three capacitance-voltage
(C-V) measurements were performed at 1 MHz over the voltage range 40 V to - 40V.
The mercury spot size was nominally 790 jim. The k values were calculated based on the
average saturation capacitance values obtained, the film thickness determined by
ellipsometry, and the mercury spot size.
The hardness and modulus of the films were measured on an MTS Nano-Indenter
XP. Due to the extreme sensitivity of the system, environmental isolation is provided
through a combination of a minus k vibration table and a thermal/sound insulated
vibration cabinet. A Berkovich diamond tip was used in the measurements with a surface
approach velocity was 10 nm/ s. The load versus displacement slope was -81.57 N/m.
All films were 500 nm or greater in thickness to minimize any substrate effects on the
results. Experiments were terminated at a depth of approximately 500 nm. The hardness
is reported at 10% of the film thickness and the modulus is taken at 50 nm.9 Fused silica
and a low-k OSG standard film were tested and used as control samples before and after
each measurement.
Thermogravimetric analysis was performed using a TA instruments TGA Q50
equipped with a Thermostar Mass spectrometer (Pfeiffer Vacuum) in the range of 50 "C
to 900 'C. As deposited p(V4D4) films were scraped into a Pt pan and purged with gas
for 15 minutes prior to beginning each run. Throughout the runs, the samples were
purged with 90 mL/min of dry nitrogen or air. Helium was used as the purge gas when
the mass spectrometer was active.
2.4. Results and Discussion
Figure 2-1 shows FT-IR spectra for both the V4D4 monomer and the iCVD thin
film. The asymmetric Si-O-Si stretching peaks located at 1075 cm-1 and 1065 cm-I
correspond to the cyclic eight-member siloxane ring in a network configuration, for the
monomer and polymer, respectively. 19 The approximately 10 wavenumber red shift
20
between the precursor and film has been observed in PECVD deposited V4D4. The lack
of broadening in this peak is consistent with the hypothesis that the iCVD process has
preserved the original cyclic siloxane ring present in the monomer precursor. Broadening
of the peak at 1065 cm-1 has previously been observed as a result of ring opening
reactions21 . Additionally, typical as-deposited PECVD thin films from cyclic siloxanes
are produced though extensive precursor fragmentation, which results in heterogeneous
Si-O bonding environments. 9,1,22 The iCVD film deposition mechanism involves freeScheme 2-la demonstrates how initiation
radical polymerization about the vinyl groups.
and propagation reactions proceed throughout iCVD deposition of V4D4, which is
analogous
to the
mechanism reported
for
1,3,5,-trivinyltrimethylcyclotrisiloxane
(V3D3).23 Film deposition through free-radical vinyl polymerization is apparent by the
reduction of the vinyl absorption bands at 960 cm-1,
1415 cm', 1600 cm-1, which
correspond to wagging and bending modes in CH 2 and C=C stretching in vinyl,
respectively.20 The simultaneous formation of polyethylene-like backbones in the iCVD
polymers is denoted by the symmetric C-H 2 stretching peaks between 2878 and 2920 cm.
Residual vinyl groups remain intact through the iCVD process and are utilized as
"built in" porogens for subsequent thermal curing steps. Table 2-1 contains a summary of
the FT-IR peak assignments from the literature.
Table 2-1: FT-IR peak assignments from the literature (v stretching, 8 bending, p
rocking, o wagging, AS antisymmetric, and S symmetric)
Peak (cm')
3056
3020
2968
2920
2878
1710-1740
1600
1470
1415
-1270
-1260
-1250
1120-1140
1065
Mode
VAS
-
CH 2
vs - CH 2
vs C-H
vs C-H
3
2
vs C-H 2
v C=O
v C=C
6 CH 2
6 CH 2
6s C-H 3
S C-H 3
S C-H 3
VAS
Comment
In vinyl groups
In vinyl groups
960
845-865
In sp CH2
In sp3 CH 2
In oxidized polyethylene
In Si-CH=CH2
Aliphatic backbone
In vinyl groups
MeSi3 'T' group
Me2SiO2'D' group
Me3SiO, unequally split
Cage SiO -Si angle~
150C in MSQ spin-on
VAS
Network Si-O-Si angle
VAS
Silicon SubOXide,
800
-780
-750
720
tCH 2
6 H-Si-O
v Si-C, PAS
v Si-C, p
VAS Si-C
vs
20
20
In sp CH3
~144 in D4 ring
1035
Reference
< 144
Si
In vinyl groups
H-SiO2 Si, network
smaller angle
D groups In SiMe 2
In SiMei
In Si-C
11,19,20,24
20
25
25
26
26
26
11,12,19,20,27-29
20
19
20
19
19
19
12
11
...................................
3500
3100
2700
2300
...
1900
wavenumber (cm-1)
= . .......
.......
1500
1100
700
Figure 2-1: FT-IR spectra for liquid V4D4 monomer and the as-deposited iCVD polymer,
p(V4D4). The gray bar highlights the position of the vinyl CH absorption. The reduction
2
of this peak in the iCVD polymer is consistent with free-radical polymerization, as is the
formation of polyethylene-like backbones between 2878-2920 cm-1. The remaining vinyl
groups are utilized as "built-in" porogens that are removed in subsequent annealing. The
lack of broadening in the Si-O-Si stretching peak indicates that the cyclic siloxane D4
ring structure has been preserved.
(a)
Si
+
/
202+
00a
~
0o
J
0'A
CH
Scheme 2-1: (a) Proposed initiation and propagation polymerization mechanism for the
iCVD p(V4D4). (b) Reaction stoichiometry required for two D4 rings to create a
substituted silsesquioxane cage structure through reaction with oxygen from the ambient
air.
the....
extensive
..... M9 cross.inking that
iCDalglcs
Thi "loosvely bound....
poymriaton....
The striking similarities between the monomer and polymer spectra indicate that
the low process power preserves the V4D4 monomer structure in the iCVD polymer. The
mild substrate temperature does not affect the chemical structure of the iCVD polymer
and is merely used as a parameter to control the deposition rate. The gentle processing
preserves the delicate organic structure, in contrast to plasma processed films, which can
lack the well-defined molecular structure of the precursor. The energy input to the iCVD
process selectively activates an initiator species and in contrast to PECVD methods, it
avoids non-selective chemistry in which unwanted side-reactions occur in parallel with
3
c
characterizes PECVD films and affords the opportunity to systematically tune the
mechanical and electrical properties of the film through subsequent thermal annealing.
Thermal annealing is a common strategy for improving the electrical and
mechanical properties of dielectric films. The low thermal-budget requirements for low-k
integration into advanced logic devices that use nickel silicide (NiSi) metal gates strictly
limits curing temperatures < 450'C.3 1 Mesoporosity and nanoporosity22 3, 2 can be
introduced into the organosilicon matrix through thermal decomposition thermally labile
organic fragments that are copolymerized with a stable Si-O skeleton. The nanoporous
voids typically contain air, which ultimately reduces the film density as well as the
dielectric constant. Thermal curing can also help improve the film's mechanical
properties by driving cross-linking reactions such as hydrolysis, 33 and condensation.9, 34 A
large degree of subtractive porosity is often incompatible with mechanically robust films.
Induced porosity in an OSG matrix will reduce the dielectric constant linearly with
density, however the mechanical properties change as a power law with density.35
Furthermore, hydrolyzation and condensation could encourage the absorption of water, k
~ 80, which increases the polarizability of the material and ultimately the dielectric
constant. Thus, optimizing the thermal annealing process becomes essential for
improving the properties of SiOCH films.
33
Drastically improved hardness and modulus have been observed in ultra low-k
PECVD films copolymerized from decamethylcyclopentasiloxane and cyclohexane
precursors that had undergone rapid thermal annealing > 450'C in oxygen ambient.36 The
oxidation of the Si-CH3 was believed increase the average film connectivity number,
which correlates with improved mechanical properties. 37 Moreover, spin-on SQ-based
films that had undergone hot plate curing in oxygen containing atmosphere demonstrated
lower dielectric constant and higher electrical breakdown strength compared to films that
had undergone standard furnace curing in nitrogen ambient.38
Figure 2-2a demonstrates the evolution of the Si-O bonding environment in the
iCVD low-k films that had undergone hotplate curing in ambient air. Figure 2-2c plots
the integrated FT-IR peak areas corresponding to the specific sub-oxide, network, and
cage Si-O bonding environments, as a ratio of the total integrated Si-O peak area (from
1000-1200 cm'). For curing temperatures < 170'C (al, a2, a3) there is visibly very little
change in the Si-O bonding environment, however the peak ratios in Figure 2-2b tend to
indicate a slight conversion from the D4 ring structure (network species), to small bond
angle sub-oxide species. Extensive oxidation of the iCVD film is not anticipated at such a
low temperature and this observation is likely attributed to a ring opening event. Even at
the modest filament temperature used in the deposition (-300'C), the D4 ring can form a
bicyclic transition state that can lead to the growth of larger siloxane rings and chains.3 9
These chains can have a structure analogous to PDMS, which has an asymmetric Si-O-Si
deformation peak at 1015cm-1 .4 More interestingly, there is a dramatic change in the SiO and Si-C (Figure 2-2b) bonding environments when the anneal temperature is
increased beyond 250'C. There is a clear conversion in the dominant Si-O network
structure, which is centered at 1065 cm' (Figure 2-2a3), to a silsesquioxane-like cage
structure in the region 1120-1140 cm 1 (Figure 2-2a4) and suboxide Si-0
2
structures at
1035 cm-1.11,19 The well-defined triplet peak in Figure 2-2a7 and the corresponding peak
area ratios in Figure 2-2c indicate that cage and suboxide features dominate the film
structure for the films cured at 410 C.
(a)
(b)
bi)
ai)
(c)
E- Cage Structure
-0- Network Structure
-A- Sub-oxide Structure
0.45
b2)
c.
0
a3)
b3
a4)
--- 0.35
b4)
00e
a5)
b5)
.
O
a6)
b6)
a7)
b7)
0.25
o--0.15
0
100
200
300
400
Anneal Temperature (OC)
1250
1150
1050
950
wavenumber (cm-i)
900
800
700
wavenumber (cm-1)
Figure 2-2: Thickness normalized FT-IR spectra for Si-O-Si stretching (al-a7) and Si-C
stretching (bl-b7), where the numbers 1-7 correspond to as-deposited p(V4D4) and
p(V4D4) annealed at 90'C, 170'C, 250'C, 330'C, 370'C, or 410'C, respectively. The
integrated peak areas for the various bonding environments in (a) correspond to specific
suboxide, network, or cage Si-O bonding, are plot as a ratio of the total integrated Si-O
peak area from 1000-1200 cm-1 (c). The primarily network structure evolves into
primarily suboxide and cage structures as the anneal temperature is increased.
Raman spectroscopy is a useful tool for examining the ring structure of cyclic
siloxane based CVD films.1 Figure 2-3 compares the Raman spectra for the as-deposited
iCVD V4D4 film, and a film that was annealed at 410'C. The Raman shift range of 160230 cm-1 corresponds to the symmetric bending of silicon bound to two carbon atoms.2 '
This peak completely disappears in the annealed film and likely indicates the complete
removal of Si-C bonds to the intact vinyl or the polyethylene-like backbones. The cured
film shows a peak at 654 cm-1, which is assigned to stretching in silicon bound to one
carbon atom 4 1 and further supports the hypothesis that the Si-C bond to vinyl was
removed by oxidation. Most significantly are the peaks at 575 and 1117 cm-1 that are
assigned to the bending and asymmetric stretching modes in Si-O-Si for organically
substituted silsesquioxane cages, respectively.
42
These peaks do not exist in the as
deposited structure, and appear in the annealed sample. Furthermore, the as-deposited and
cured films share Raman bands between 490-495 cm-1, which corresponds to symmetric
bending of Si-O-Si in the cyclic D4 ring. 2 1 This is additional evidence that the iCVD
process preserves the cyclic nature of the precursor and that this structure survives the
curing process. Moreover, this also indicates that certain facets of the silsesquioxane-like
cages in the cured films consist of intact D4 rings. Scheme 2-lb represents the reaction
stoichiometry required for two D4 rings within the film structure to create a substituted
silsesquioxane cage structure through reaction with oxygen from the ambient air. Table
2-2 contains a summary of the Raman shift assignments from the literature.
Table 2-2: Raman shift assignments from the literature (v stretching, 6 bending, p rocking,
AS antisymmetric, and S symmetric)
Raman Shift (cm-1)
1117
800
795
758
VAS
Mode
Si-O-Si
Si-(CH3 ) 2
C-Si-C
VAS, Si-C
VAS
p s Si-(CH3)3
654
575
p me, VsiC Si-(CH3 )
6 O-Si-O
490-495
6S Si-O-Si
400, 425
160-230
vs Si-Si
6s C- Si-C
Comment
Organically substituted
SSQ cages
PECVD HMDSO
In SiC 2
In PDMS and/or PECVD
HMDSO
PECVD HMDSO
Organically substituted
SSQ cages
D4 ring in vitreous and/or
CVD silica
In HWCVD D4
In D4, PDMS
Reference
As Deposited:
Annealed
@a)410*'C
1150
950
750
550
350
150
Raman Shift (cm-1)
Figure 2-3: Raman spectra of p(V4D4) films as-deposited and annealed at 410'C. The
preservation of the cyclic D4 structure is evident by the peak at 495 cm-1. The peaks at
575 and 1117 cm-1 that appear in the annealed structure correspond to Si-O-Si
stretching in organically substituted silsesquioxane cages.
42
41
21
41,43
41
42
21
21
21,41
In consideration of a mechanism for the systematic formation of the SQ type
cages, we further examine the FT-IR spectra in Figure 2-2b. When the Si-O region in the
cured film transitions between a network and a cage structure (Figure 2-2a3 and Figure 22a4) there is a simultaneous reduction in the bands at 750 and 800 cm' (Figure 2-2b3)
corresponding to asymmetric stretching in Si-C
groups within a DCH(CH 2 )xgroup'
19
12
and asymmetric rocking in methyl
[0 2 Si(CH 3)(CHCH 2)], respectively. The simultaneous
reduction of these bands is accompanied by the appearance of a sharp band at 780 cm',
Si-CH3 rocking in 'T'groups,19 [03Si(CH 3 )i], and a broad band between 845- 865 cm'
that represents H-Si-O bending in small bond angle Si0 2 .19 The intensity of these bands
increase as the curing temperature is varied from 250-410'C (Figure 2b4-2b7). A D4 ring
must lose one Si-C bond and form an additional Si-O bond in order to form the facet of
a cage. Thus, the destruction of DCH(CH 2 )x and subsequent oxidation of 02Si(CH 3)* would
create this 'T' group. The destruction of this bond mirrors the reduction and eventual
elimination of vinyl stretching and aliphatic backbones, which was indicated by FT-IR
(not shown). The SiCH 3 bonds stabilize the SQ structure, 33 and are less likely to undergo
oxidation than the Si-C bonds to the unreacted vinyl groups and the aliphatic
hydrocarbons corresponding to the polyethylene-like backbone. 9 '44
The FT-IR spectra in Figure 2-4a specifically illustrates how the as-deposited
V4D4 films evolve crosslinks as the film becomes oxidized. Within the 1250-1280 cm'
range are found three peaks that correspond to bonding environments of silicon that have
undergone various degrees of oxidation.9 The as-deposited structure (Figure 2-4al)
demonstrates a strong C-H
3
symmetric bending peak at 1260 cm', which is specific to
'D' groups, 02Si(CH 3 )2 . This reflects the inherent degree of oxidation in the V4D4
precursor, in which two chain propagating oxygen atoms are bound to silicon, and
supports the earlier assertion that the as-deposited film is held together by polymerized
polyethylene-like backbones, and not by additional oxidation of the D4 rings. This 'D'like character is preserved within the films annealed at 90 and 170 'C (Figures 2-4a2 and
2-4a3, respectively). For the film annealed at 250'C, a transition is observed in the
bonding structure. The peak has shifted to the symmetric C-H
3 bending
mode -1270 cm
1 (Figure 2-4a4), which corresponds to 'T' groups, 0 3 Si(CH 3 ); however, the broad
shoulder of the peak extends to the ~1260 cm-1 region. The broadness of the peak
indicates that the bonding environment in this film is evenly distributed between 'D'
group and 'T' groups. These 'T' groups are a crosslinking structure in which silicon is
bound to three network forming oxygen atom. Furthermore, this represents the onset of
Si-C oxidation to form a facet of an SQ cage, as discussed earlier. The degree of silicon
oxidation is further enhanced by increasing the anneal temperature to 410'C. Figure 24a5- 4a7 show how increasing the anneal temperature causes the 'T' group peak at -1270
cm-1 to narrow until no more 'D' structure is indicated. No IR activity was observed for
singly oxidized silicon 'M' groups OSi(CH 3)3 , which peak at 1250 cm-1.
9,11,12
(a)
al)
a2)
*0.10
2(b)
a3)
0.08
0N
a4)
a6)
C 0.06
N.
a5)
in
a6)
EN
:0.04N
N
11
a7)
0.02
0
1290
1270
1250
wavenumber (cm-1)
100
200
300
400
Anneal Temperature ('C)
Figure 2-4: Thickness normalized FT-IR for the Si-CH bonding region for as deposited
3
p(V4D4) and films annealed at 90'C, 170'C, 250'C, 330'C, 370'C, or 410'C (al-a7).
Peaks at 1262 and 1272 cm-1 correspond to 'D' and 'T' groups, respectively. The general
trend demonstrates that the degree of silicon oxidation increases as the anneal
temperature is increased. The ratio of the integrated Si-CH region (1250-1280 cm-1) to
3
the total integrated Si-O peak area from 1000-1200 cm-1 (b) suggests the incorporation of
'Q' groups (fully oxidized silicon atoms).
One would expect that removal of, or Si-C bond breaking in, the more labile
CxHy species"
associated with polymerized and intact vinyl groups would convert all
of the 'D' groups to 'T' groups. However, we must also consider the oxidation of
Si-CH3 bonds, leading the formation of 'Q' groups (silicon quad-substituted with
oxygen). These groups represent fully crosslinked Si-O bonds and correspond to the
evolution of small angle suboxide species. They are anticipated to bridge the connections
between stable SQ cages 29 and provide the films with mechanical robustness. As 'Q'
groups contain no Si-C bonds, is not possible to directly measure their presence within
the 1250-1280 cm-1 region. Figure 2-4b compares the ratio of the integrated Si-CH3 area
to the total Si-O area that was determined by FT-IR. There is an observed trend of CH 3
loss as the anneal temperature is increased. By assuming that the Si-CH3 groups are the
more stable Si-C bonds in the as deposited film, this observation indirectly suggests that
a fraction of the silicon bonds in the films cured at higher temperatures are in fact
crosslinking 'Q' groups. We can quantify the presence of 'D', 'T', and 'Q' groups in each
film through connectivity number analysis. This technique is built on the framework of
continuous random network theory46 and has been previously demonstrated as a useful
technique for exploring the relationship between the structural and mechanical properties
of cross linked low-k films. 9' 34 ,46 The connectivity number measures the average ratio of
network forming bonds to network forming atoms in a polymeric thin film. The
percolation of rigidity occurs at a connectivity number of 2.4. When the average film
connectivity is below the percolation threshold, the network solid is considered a non
rigid polymeric glass; above the threshold, the solid becomes rigid and amorphous, which
translates to significantly improved mechanical properties. The percolation of rigidity for
low-k films from the cyclic siloxane precursor octamethylcyclotetrasiloxane was
observed at a connectivity number between 2.35-2.4.34 Connectivity numbers of 2.2, 2.4,
and 2.67 are ascribed to 'D', 'T', and 'Q' groups, respectively. Thus, a film containing
100% 'T' groups is necessary to reach the percolation threshold. Figure 2-5a plots the
connectivity numbers for the iCVD V4D4 films.
These values were determined by
deconvoluting the peak areas for 'T' and 'D' group contributions from the normalized
FT-IR spectra in Figure 2-4a. Because the spectra are thickness normalized, each
spectrum is assumed to reflect an identical quantity of silicon atoms. 34 The as-deposited
film is assumed to have no 'Q' groups, which is corroborated by the FT-IR data in Figure
2-1. Since each silicon atom exists in either a 'T', 'D' or 'Q' configuration, any
difference in the total normalized SiCH 3 area for the annealed films is attributed to the
formation 'Q' groups. The calculated connectivity number is simply the sum of the
weighted contribution from each group. There is a very slight increasing trend in the
connectivity number of films annealed < 250'C, however all these values are below the
percolation threshold. For the film annealed at 250'C, the connectivity value -2.2
indicates that the film properties are approximately half 'T' and half 'D'. Increasing the
anneal temperature past 250'C boosts the connectivity past percolation threshold. The
film properties reflect 'T' and 'Q' bonding structure, 47 as these films contain no 'D'
groups. Figure 2-5b shows the measured values of hardness and modulus for the annealed
films. The films annealed at 410'C demonstrate greater than five fold increases in film
hardness (from 0.15 GPa to 0.79 GPa) and greater than 1.5 fold increase in the modulus
(from GPa 3.48 to 5.42 GPa). The film hardness is practically unchanged below 210'C
and all films with connectivity numbers above the percolation threshold had hardness
values greater than 0.5 GPa. Therefore, the higher annealing temperatures drive oxidation
reactions that increase the film connectivity beyond the percolation of rigidity, which
significantly enhances the mechanical properties of the films.
5.50
0.90
2.55
(b)
(a)
2.45
-Q
E 2.54.50
-
Percolation
Threshold
0.70
Ca
0
C
:3 2.35
zE
E
0.50
a
C-
*4.00
-7-2.25
2
cc
C
0
0.30
U 2.15
3
2.05
0
100
.
200
'.
.
.
300
Anneal Temperature (0C)
..
400
3.50
.
0.10.
0
.
100
.
.
200
.
300
.
.
400
3.00
Anneal Temperature (OC)
Figure 2-5: Average film connectivity number plot versus anneal temperature (a). Films
annealed at temperatures below 330'C have connectivity below the percolation threshold.
The mechanical properties for the cured p(V4D4) (b) reflect drastically increased
hardness and modulus as the films approach a connectivity greater than 2.4.
The crosslinking mechanisms we have discussed simultaneous act to reduce the
density of the cured films. The formation of SQ cages throughout the curing process
generates a greater free volume in the film skeleton and introduces intrinsic porosity.29
Furthermore, the removal of thermally labile hydrocarbon fractions represents an induced
porosity. Figure 2-6a plots the refractive index of the cured films. There is a slight
reduction in the refractive index for films cured < 170'C, after which there is a dramatic
monotonic decrease in the refractive index as a function of cure temperature.
Thermogravimetric analysis of the V4D4 films (available as supporting information)
shows a significant mass loss event at 198'C. This is within the same temperature range
over which the most dramatic structural changes were observed by FT-IR. Thus, this
transition in film density likely results from the combined effects of removing unstable
organic species and forming cross linked SQ cages. Assuming that void spaces in the
films are filled with air, the Lorentz-Lorentz equation 4 8 gives the relationship between the
film porosity, P, and optical properties by:
2
nF
F2
P
1-
where n,2porous and n2as
n porous
nLporous
2,, +2
+2
dep
L
(2-1)
as dep
2,, +2
nporous+2
are the refractive index for the cured films and as-deposited films,
respectively. Figure 2-6b plots the calculated film porosity as a function of anneal
temperature. There is a monotonic increase in film porosity as the annealing temperature
is increased. This trend would indicate that the dielectric constant should decrease
monotonically with porosity, 49however, the observed trend for the dielectric constant is
more complicated.
25
1.51
(a)
(b)
1.48
,'
20-
-01.45/
1
C
0/
1.42
0
10
4)~
/
1.39
/*&
1.36
1.330
0
100
200
300
400
Anneal Temperature (*C)
0
100
200
400
300
0
Anneal Temperature ( C)
Figure 2-6: Refractive index for various cured p(V4D4) films (a). The porosity (b) was
calculated using the Lorentz-Lorentz equation (2-1).
Figure 2-7a plots the measured dielectric constant as a function of anneal
temperature. There is a slight increase in the dielectric constant between the as-deposited
film and the films and the films annealed at 90 and 170'C. The dielectric constant then
follows a parabolic trend with a maximum k value of 3.53 and minimum k value of 2.15,
which correspond to the samples annealed at 250'C and 410'C, respectively. This
counterintuitive observation could be explained by examining the evolution of highly
polarizable species within the film. Figure 2-7b shows the FT-IR stretching region
between 1710-1740 cm', which corresponds to C=O stretching."
24
The evolution of
carbonyl groups mirrors the parabolic trend of the dielectric constant. Although the
sample annealed at 250'C corresponded to a drastic reduction in film density, this sample
also demonstrates a high degree of carbonyl incorporation. Carbonyl groups are polar
substituents that contain high orientational polarizability.' The dielectric constant of a
material is commonly described by the Clausius-Mossotti equation: 29
(k - 1)
(k- )
(k+2)
4z
3 Na
3
(2-2)
where k is the material dielectric constant, N is the number of molecules per unit volume
(density) and a is the total material polarizability, which includes orientation, electronic,
29
and distortion polarizabilities. This expression shows that the dielectric constant can be
increased even if the film density is reduced, simply by incorporating highly polarizabile
substituents such as carbonyl. Therefore, it follows that the observed k value reflects this
trend, thus, carbonyl formation is not desired. The mechanism for carbonyl formation is
likely analogous to the oxidation of polyethylene, 50 which is a commonly observed
phenomenon in the aging of plastics. The polyethylene-like backbones in the iCVD
polymer are thus predisposed to oxidation, and their omnipresence in the as deposited
film makes them a target for carbonyl incorporation at higher curing temperatures.24
Fortunately, the high temperature instability of the carbon backbones allow for their
removal upon annealing at 410'C. This temperature is within the thermal budget for a
BEOL process and results in a film with a dielectric constant value of 2.15. This film
corresponds to the best mechanical properties and shows that improvement in modulus
and hardness and reduction of dielectric constant occur simultaneously in the iCVD
p(V4D4) films annealed in ambient air. Figure 2-8 compares the best dielectric constant
and modulus from this study with previously reported results of merit for low-k OSG
95
films. ' 1-54
(b)
b1)
b2)
3.50
b3)
(a)/
3.20
/
C
02.90
b4)
2.60
b5
2.30
b6
2.00
0
100
200
300
400
Anneal Temperature (4C)
1850
1750
1650
wavenumber (cm-1)
Figure 2-7: The dielectric constant is plot versus anneal temperature (a). The parabolic
shape is attributed to the evolution of highly polarizable carbonyl bonds, C=O. The plot of
the 1710-1740 cm-1 FT-IR spectral region (b1-b7) indicates that the largest carbonyl
incorporation occurs at an anneal temperature of 250'C (b4), which corresponds to the
highest dielectric constant. The dielectric constant reflects that the reduction in film
density is offset by the increased bond polarizability.
6.5
6.0
-
5.5 -
CL
S 5.0
U)
-o
4.5
0
+
4.0
)K
3.5 -A
3.0
2.0
2.1
2.2
2.3
2.4
2.5
2.6
Dielectric Constant
Figure 2-8: A comparison between the best dielectric constant and modulus from this
study with previously reported results of merit for low-k OSG films. 9,51-54
The silicon, oxygen, and carbon composition of the films was carefully examined
with XPS. Survey scans were performed for each film and Table 2-3 shows the percent
composition of silicon, oxygen, and carbon in the various cured films. Previous studies
from our group on the bonding structure of SiOCH films, used XPS to determine the
elemental ratios that would be expected for various bonding environments. 5 A film
comprising of only 'T' groups would contain 28.6%, 28.6%, and 42.8% carbon, silicon,
and oxygen, respectively. A film containing pure 'Q' character would contain 33.3%
silicon and 66.66% oxygen. Assuming that the V4D4 film cured at 410'C contains only
'T' and 'Q' groups, the relative contribution calculated from a weighted sum of atomic
contributions is 83% 'T' groups and 17% 'Q' groups. This corresponds to 23.780%
carbon, 30.447% silicon, and 46.856% oxygen. Our experimentally determined atomic
compositions for the sample cured at 410'C in Table 2-3 are within 1%of these values.
Therefore, the elemental composition for our cured films supports our other experimental
observations suggesting that the fully cured structure exists primarily as SQ cages ('T'
groups) that are interconnected with fully crosslinked 'Q' groups.
Figure 2-9
demonstrates a proposed molecular visualization of such a structure.
Figure 2-9: Proposed molecular model for the cured V4D4 films, which consist of MSQ
cages interconnected by crosslinking 'Q' groups.
Table 2-3: Atomic compositions calculated from XPS survey scans for various annealed
V4D4 films. The values corresponding to annealing at 410'C are within 1% of the theoretical
value for a film containing 83% 'T' groups and 17% 'Q' groups.
Atomic %
Carbon
As Dep
52.584
90 0 C
52.414
170 0 C
51.862
250 0 C
39.266
330 0 C
30.343
410 0 C
23.585
Oxygen
25.616
25.797
26.460
33.646
38.413
45.754
Silicon
21.800
21.789
21.677
27.089
31.244
30.661
The XPS data also agrees with the notion that carbon is systematically removed as
the anneal temperature is increased. Figure 2-10 plots the elemental ratios of carbon to
silicon (8a) and carbon to oxygen (8b) as a function of anneal temperature. The elemental
composition of the V4D4 films remains essentially unchanged below 170 0 C. Between
170 0 C and 250 0 C, the films lose a significant quantity of carbon, which is consistent with
the trend in refractive index reported in Figure 2-6. Furthermore, thermo gravimetric
analysis shows the onset of a significant mass decomposition event at 335'C. This mass
loss trend continues through to the final curing temperature of 410'C and is represented
well by the XPS ratios in Figure 2-10.
2.20
2.50
(a)
1.80
(b)
20
1.40
1.50
1.00
1.00
0.60
0.20
0.50
0
100
200
300
Anneal Temperature (*C)
400
0
100
200
300
400
Anneal Temperature (*C)
Figure 2-10: The elemental ratios of carbon to silicon (a) and carbon to oxygen (b) plot
versus anneal temperature. The films lose a significant amount of carbon between 170'C
and 250'C, as was suggested by the refractive index trend in Figure 2-6a.
2.5. Conclusions
We have demonstrated that thermal oxidation of iCVD p(V4D4) in atmospheric
ambient both can simultaneously enhance the mechanical properties and reduce the
dielectric constant of the cured films. The as-deposited polymer retains the delicate
organic functionality and structure of the monomer precursor and the systematic
oxidation of the D4 rings produces an SQ type cage structure, which is indicated through
the formation of 'T' groups. Raman spectroscopy confirms that the D4 ring structure is
preserved throughout the curing process and likely makes up the facets of the SQ cages.
Annealing allowed us to benefit from the high degree of intrinsic porosity of SQ cages,
which is attributed to their great free volume. Complete oxidation of the silicon creates
'Q' groups, which impart greater hardness and modulus to the films. The removal of
labile hydrocarbon moieties allows for the oxidation of the as-deposited film while
simultaneously introducing induced porosity. Although the oxidation of the polyethylene-
like backbones creates highly polarizable carbonyl bonds between 250'C and 350'C,
they are eventually removed at higher temperatures. Overall, the best films properties
occur for an anneal temperature of 410'C, which corresponds to approximately 83% 'T'
groups and 17% 'Q' groups, as confirmed by XPS analysis. While typical processes
trade-off mechanical and electrical properties, improvement in modulus and hardness and
reduction of dielectric constant occur simultaneously in the iCVD p(V4D4) films
annealed in ambient air. The measured dielectric constant and hardness for this film was
2.15 and 0.78 GPa, respectively. Thus, the all dry, low energy iCVD process is an
environmentally focused process that is capable of producing low-k films with attractive
mechanical and electrical properties by curing at temperatures that are within the BEOL
thermal budget.
2.6. Acknowledgements
The authors acknowledge the support of the NSF/SRC Engineering Research
Center for Environmentally Benign Semiconductor Manufacturing. This work made use
of the MRSEC Shared Experimental Facilities supported by the National Science
Foundation under award number DMR - 0819762 and the XPS facility at the Cornell
Center for Materials Research (CCMR) with support from the National Science
Foundation Materials Research Science and Engineering Centers (MRSEC) program
(DMR - 0520404). We gratefully acknowledge Dr. Jonathan Shu of Cornell University
for assistance with XPS.
2.7. Supporting Information
Thermogravimetric analysis was performed on p(V4D4) films. Two different
annealing environments are represented. The dotted trace represents nitrogen purged
annealing. The solid trace represents annealing with an ambient purge. For both runs,
there are three significant mass loss events. The first two events occur at the same onset
temperatures. RGA analysis shows that the vinyl groups make up the majority of these
decomposed species. At elevated temperatures the thermal stability is much greater with
the nitrogen purge; the third decomposition event occurs at 335'C for the sample
annealed in air, versus 475'C for the sample annealed in nitrogen. This event primarily
represents increased oxidation and displacement of the stabilizing methyl groups, as
indicated by RGA. The higher stable mass for the oxidized sample confirms that oxygen
was indeed incorporated into the structure.
100
0.9
-
Annealed in air
- - - - Annealed in N2
90
80
0.6
0)
E
>
0O
70
6
60
0.3
so
50
40
-0
0
100
200
300
400
500
600
700
Anneal Temperature (OC)
Figure 2-Si: TGA mass evolution for p(V4D4) films annealed under two different
annealing environments. The peaks in the bottom two traces correspond to the respective
temperatures for decomposition onset.
...
....
.............
..............
..
.. ..
. ..
.....
.............
.
Table 2-Si: Proposed fragments released during pyrolysis by TGA
Assignment
CH 3+
H20
CH 2=CH*
O=CH*
H2C=C=CH*
m/z
15
18
27
29
39
44
56
1.OOE-09
CO2
C4H8
Corresponding Anneal
Temperature
120 *C 200 OC
475 0C
-Mass
39
Mass 73
-Mass
30
-Mass
18
-Mass
91
-Mass
44
Mass 56
Mass 27
-Mass
26
-Mass
15
-Mass
29
1.00E-10
1.00E-11
o
1.OOE-12
1.OOE-13 "
0
10
20
40
30
50
60
70
80
Time (minutes)
Figure 2-S2: Temperature evolution of various ions detected by residual gas analysis
(RGA). Helium was used as the purge gas.
2.8. Technical Notes on Deposition Parameters for iCVD p(V4D4)
iCVD process kinetics are generally absorption limiting and the rate determining
parameter is the net monomer surface concentration.16 Figure 2-Ni shows an Arrhenius
plot of the p(V4D4) deposition rate as a function of substrate temperature. The dark
diamonds represents the polymer thickness measured during the deposition by
interferometry while the open squares represent the film thickness measured by
ellipsometry. Interferometry measures the thickness of the as-deposited layer in the
vacuum chamber. This layer may contain both polymerized material and entrained
monomer. The entrained monomer may desorb from the film during the post-deposition
evacuation of the vacuum chamber and during post-deposition annealing. The thickness
of the stable portion of the film remaining on the substrate is measured by ellipsometry.
Differences between the thicknesses measured by in-situ interferometry and by ex-situ
ellipsometry most likely indicate the loss of entrained monomer. After evacuating the
chamber, significant outgassing from the stable polymer film is indicated by a change in
the film color. For the early region of the plot, corresponding to the highest substrate
temperatures, the two data series compare well with one and other. This indicates a stable
film, with little to no entrained monomer. In this substrate temperature range the
calculated activation energy is -49.30 kJ/mol, which corresponds to a heat of desorption
of 24.90 kJ/mol. This is within 20 kJ/mol- 80 kJ/mol range required for the physisorption
of small molecules through Van der Waalls forces.56 The negative activation energy is
consistent with an adsorption limiting process, and this trend follows through the entire
diamond data series. However, for lower substrate temperatures (below 30"C) there
appears to be a large difference between the stable polymer thickness measured by
ellipsometry and the thickness measured by in-situ interferometry. This means that the
polymer deposition rate is actually less than the rate of monomer adsorption; this causes
monomer to become entrained. This also suggests that there has been a transition between
adsorption limiting kinetics to reaction limiting kinetics, and forming a stable polymer
film becomes the slowest step.
.
....
......
_.I.-...............
.................
...........
....
.. ..
..........
...............
....................
Ts (Kelvin)
138
323
328
333
318
313
308
3.20
3.25
3.00
#
Interferometry Thickness
0 Elipsometry Thickness
2.50
2.00
*
i 00 "
-
2.95
-
-
-
*l
-
3.00
-
-
-
-
3.05
-
-
3.10
1/Ts (x
3.15
OA-3KA-1)
Figure 2-N1: Deposition rate data for polymer film growth as a function of substrate
temperature. The diamonds represent the deposition rate as measured in-situ by
interferometry and the open squares represent the film thickness measured ex-situ by
ellipsometry.
A separate set of experiments was conducted to explore deposition rates over a
range of operating pressures (Figure 2-N2) and similar trends were observed. For low
reactor pressures there is almost perfect agreement between the in-situ and ex-situ
thickness measurements. These results are consistent with second-order kinetics observed
in free radical polymerization.5 7 At high pressures there is a dramatic reduction in the
stable film deposition rate measured by ellipsometry. This rate is about 1/3rd the rate
..........
...... .
. ......
.
...
. ......
...........
.
... ..........
. .. ...........
measured by interferometry, presumably indicating a large volume of entrained
monomer, and about 1/2 the deposition rate observed at a lower reactor pressure. It was
difficult to test this concept at lower substrate temperatures or higher reactor pressures
since the process window for polymer deposition without condensation was too narrow.
Table 2-Ni contains a summary of the reactor conditions used for the deposition rate
experiments depicted in Figures 2-NI and 2-N2.
* Interferometry Thickness
o Elipsometry Thickness
5
0
0.03
0.05
0.07
0.09
0.11
0.13
Pm/Psat
Figure 2-N2: Deposition rate data for polymer film growth as a function of monomer
partial pressure as a fraction of saturation. The diamonds represent the deposition rate as
measured in-situ by interferometry and the open squares represent the film thickness
measured ex-situ by ellipsometry.
Table 2-N1: Reactor conditions for deposition of iCVD p(V4D4) films
Monomer
Flowrate
(sccm)
Initiator
Flowrate
(sccm)
585 ±4
0.5
1.0
323 ±1
585 ±4
0.5
1.0
653 ±2
330 ±1
585 ±4
0.5
1.0
T4
653 ±2
338 ±1
585 ±4
0.5
1.0
P1
319 ±2
323 ±1
595 ±3
0.5
1.0
P2
658 ±2
323 ±1
595 ±3
0.5
1.0
P3
932 ±2
323 ±1
595 ±3
0.5
1.0
P4
1104 ±2
323 ±1
595 ±3
0.5
1.0
Filament
Stage
Temperature Temperature
(Kelvin)
(Kelvin)
Sample
Name
Reactor
Pressure
(mTorr)
TI
653 ±2
313 ±1
T2
653 ±2
T3
2.9. Technical Notes on Porogen use with p(V4D4)
Hybrid materials with low dielectric constants are created by copolymerization of
cyclic precursors with sacrificial organic materials, to create a nanoporous matrix. 13
22,59
58
cyclopentene oxide,"
Materials such as dextran, 8 PMMA,4 9 norbornene,
and
terpinene 22,59 have been successfully used as porogens, to achieve k values as low as
2.05.11 Most these porogen molecules are either cyclic unsaturated hydrocarbons, or
linear alkenes;2 however, small changes in chemical composition can result in large
differences in incorporation and removal efficiencies upon annealing. Cyclopentene
oxide and norbornadiene have been identified as the two most promising porogen
precursors to allow preservation of electronic and mechanical properties after anneal.59
The mechanical properties of SiCOH dielectrics generally decrease with lower k
values ,9,37 and typically scale with porosity as (1-p)3 I until the percolation point, where
pores coalesce. 60 Condensation reactions by thermal curing 9 34 and bond rearrangement
through ultraviolet cure61-63 can help improve these mechanical properties.
In order to further examine the effects of porosity on the electrical properties of
the iCVD low-k film, the V4D4 monomer was copolymerized with a variety of pororgen
precursors. The porogens evaluated include two distinct methacrylate monomers,
cyclohexyl methacrylate (CHMA) and isobornyl methacryate (IBMA). An additional
aromatic porogen, terpinine, was physically incorporated into polymerized iCVD film
through non-covalent interactions. Figure 2-N3 shows the FT-IR spectra for various
hybrid low-k films. Figure 2-N3a corresponds to a CHMA:V4D4 flow ratio of 0.5:1,
whereas figure 2-N3b represents a CHMA:V4D4 flow ratio of 2. Figure 2-N3c
corresponds to the hybrid films copolymerized from IBMA and V4D4 precursors at a
flow ratio of 2:1. The most distinctive characteristic for each spectrum is the relative
height of the carbonyl peak between 1720-1740 cm-1, which increases proportional to the
porogen content in the hybrid films. As the p(V4D4) film does not contain any carbonyl
in the as-deposited structure, this observation indicates that the porogen precursor has
been copolymerized within the growing p(V4D4) chains. Terpinene does not contain any
distinguishing FT-IR features that are captured in the hybrid low-k film (figure 2-N3d).
. ...
.......................
.
......
As Deposited Fil
ns
C=O
a) V4D4-co -CHMA
_Job) V4D4-co -CHMA
c) V4D4-co -LIBMA
d) V4D4/ Terpinene
3200
2700
2200
1700
1200
Wavenumber (cm-')
Figure 2-N3: FT-IR spectra for hybrid iCVD low-k copolymer films produced from V4D4
precursors and CHMA (a)(b), IBMA (c), and Terpinene. The grey bar highlights the
position of the carbonyl peak between 1720-1740 cm-1.
The growth rates for the low-k copolymer films were much greater than for the
p(V4D4) homopolymers, with copolymer deposition rates ranging from 20-25 nm/min.
This rate enhancement has been reported for copolymers from V3D3 and linear spacer
molecules.64 Figure 2-N4 shows the porosity, calculated using the
Lorentz-Lorentz
equation 48 , for various p(V4D4-co-CHMA) copolymer films annealed in air. When
compared to the as-deposited homopolymers, there is only a slight increase in the overall
film porosity for the hybrid films at each anneal temperature. The hybrid films with a
CHMA:V4D4 ratio of 2:1 should theoretically contain four times more CHMA than those
films with a flow rate ratio of 0.05:1; however, the porosity is only slightly higher than
for the homopolymer film. This is likely attributed to disparity between the
.
..
.. ........
....
.....
decomposition temperatures of the porogen and the decomposition of the unstable
organic fragments from the V4D4 component.
(0
0.
0
0.0
250
330
410
Annealing Temperature ("C)
Figure 2-N4: Calculated porosity for p(V4D4-co-CHMA) hybrid films annealed in air at
various temperatures.
Figure 2-N5 shows the TGA decomposition profiles for as-deposited and hybrid
V4D4 films, and CHMA annealed in air. The helium decomposition profile for the
p(V4D4) has been included for comparison.
...
........................
...
....................
100
0As
dep. in helium
80
70
As
60
dep. in
air
-
Hybrid
50
40
p(CHMA)
30
20
10
0
100
200
300
400
500
600
700
Annealing Temperature (*C)
Figure 2-N5: TGA mass decomposition profiles for as-deposited and hybrid V4D4 films
annealed in air or helium.
The decomposition profile for the hybrid film indicates a much smaller stable mass at
400*C when compared to the homopolymer. At first glance, this would suggest that the
porous copolymer film should contain greater porosity than the homopolymer film
annealed under the same conditions. However, figure 2-N4 seems to contradict this.
Figure 2-N6 depicts the overall film shrinkage for the various V4D4-co-CHMA
copolymer films.
...............
. ............
70
60
Hybrid
;.-
C
-
I) 40
As dep.
30
20
300
250
350
400
Annealing Temperature (0C)
Figure 2-N6: Overall film shrinkage for various V4D4-co-CHMA copolymer films
annealed in air. The diamond and triangle series corresponds to CHMA:V4D4 ratios of
2:1 and 0.5:1, respectively.
The overall thermal stability of the film is greatly reduced in the hybrid films. The
smaller stable mass observed in figure 2-N5 directly reflects this overall film shrinkage
and does not directly correspond to an increased porosity. The decomposition profile for
the hybrid film indicates that a majority of the film decomposition occurs around 280*C,
which is a significantly lower temperature than 330*C, where a large degree of oxidation
is anticipated to occur. Therefore, it is likely that the cooler decomposition temperature of
the porogen phase (CHMA) causes the V4D4 component of the copolymer to become
unstable prior to the onset of stabilizing oxidation reactions, resulting in poor overall
thermal stability.
............
...........
.. ..
..........................
..................
....
..
..
..........
The annealed hybrid films do not demonstrate a reduced dielectric constant over
the homopolymer films annealed at 410"C. Figure 2-N7 plots the dielectric constant
versus anneal temperature for the various V4D4-co-CHMA copolymer films.
3.50
P ,
Hybrid
3320
_-A
2.90
As dep.
2.60
2.30
2.00
0
100
200
300
400
Annealing Temperature (*C)
Figure 2-N7. Dielectric constant versus anneal temperature for various V4D4-co-CHMA
copolymer films annealed in air. The diamond and triangle series corresponds to
CHMA:V4D4 ratios of 2:1 and 0.5:1, respectively.
The increased dielectric constant is attributed to the increased carbonyl content within the
hybrid films. Between 200*C and 350"C the carbonyl content attributed to oxidation of
the polyethylene-like backbones in the V4D4 component likely exceeds the carbonyl
incorporation
from the CHMA component, which explains why the annealed
homopolymer has a larger dielectric constant within this temperature range. Although
there does not appear to be any residual carbonyl groups in the hybrid films from CHMA
and IBMA porogens annealed at 410"C, FT-IR depicted in figure 2-N8, the dielectric
constants at 410"C are significantly greater than for the homopolymer films.
.
.........
... .. .....................................
-
......
......................
...........
....
....
Annealed in air for 1hr @ 410*C
a) V4D4
b) V4D4-co-CHMA
04a
3200
A
V4D4-co-IBMA
A Who- Ow".
2700
2200
0-11,
1700
1
1200
700
Wavenumber (cm-1)
Figure 2-N8: FT-IR spectra for iCVD low-k homopolymer (a) and copolymer films
annealed in air and produced from V4D4 precursors and CHMA (b), or IBMA (c).
When hybrid films were annealed in nitrogen, no improvement was observed in
the dielectric constant and film stability over the homopolymer films. Figure 2-N9 shows
the FT-IR spectra for the homopolymer and hybrid films annealed at 400"C under
nitrogen ambient.
3200
2700
2200
1700
1200
700
Wavenumber (cm-1)
Figure 2-N9: FT-IR spectra for iCVD low-k homopolymer (a) and copolymer films
produced from V4D4 precursors and CHMA (b), or IBMA (c).
In summary, the best overall iCVD low-k films result from p(V4D4)
homopolymers annealed in air at 400"C. Copolymerization to form a hybrid film results
in a greater dielectric constant and reduced thermal stability compared to the
homopolymer. Table 2-N2 summarizes the thermal and electrical properties for several
sets of annealed and as-deposited hybrid and homopolymer V4D4 films.
Table 2-N2: Summary of electrical, optical, and thermal performance for various as
deposited and annealed hybrid and homopolymer V4D4 films.
Refractive
Dielectric
Percent
Environment
Index
Constant
Shrinkage
V4D4 as dep.
--
1.470
2.70
--
V4D4 as dep.
V4D4 as dep.
Air
Nitrogen
1.345
1.440
2.15
2.71
45%
6%
V4D4-co-CHMA 1:2
--
1.482
3.15
--
V4D4-co-CHMA 1:2
V4D4-co-CHMA 1:2
Air
Nitrogen
1.342
1.460
2.54
3.01
67%
42%
V4D4-co-CHMA 2:1
--
1.478
2.99
--
62%
System
Anneal
V4D4-co-CHMA 2:1
Air
1.346
2.66
V4D4-co-IBMA 1:2
--
1.479
--
--
Air
Nitrogen
1.359
1.450
---
64%
50%
V4D4-co-Terpinene
--
1.460
--
--
V4D4-co-Terpinene
Nitrogen
1.455
--
61%
V4D4-co-IBMA 1:2
V4D4-co-IBMA 1:2
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M. Yoshioka and T. Otsu, Macromolecules 25, 2599-2602 (1992).
J. H. Yim, H. D. Jeong, and L. S. Pu, Thin Solid Films 476, 46-50 (2005).
59
S. Bilodeau, P. Chen, W. Giannetto, C. Xu, W. Hunks, T. H. Baum, and J. F.
Roeder, in Porogen Precursorsfor ULK (k<2.2) PECVD Dielectrics, San Diego,
60
61
62
63
64
CA, 2006 (Warrendale Pa; Materials Research Society; 2007), p. 367-374.
J. Liu, D. Gan, C. Hu, M. Kiene, P. S. Ho, W. Volksen, and R. D. Miller, Applied
Physics Letters 81, 4180-4182 (2002).
F. lacopi, G. Beyer, Y. Travaly, C. Waldfried, D. M. Gage, R. H. Dauskardt, K.
Houthoofd, P. Jacobs, P. Adriaensens, K. Schulze, S. E. Schulz, S. List, and G.
Carlotti, Acta Materialia 55, 1407-1414 (2007).
J. M. Jacques, T. Y. Tsui, A. J. McKerrow, and R. Kraft, Materials Research
Society Symposium Proceeding 914 (2006).
R. S. Smith, T. Tsui, and P. S. Ho, Materials Research Society Symposium
Proceeding 990 (2007).
A. K. H. Achyuta, A. J. White, H. G. Pryce Lewis, and S. K. Murthy,
Macromolecules 42, 1970-1978 (2009).
Chapter 3
Multi-scale grafted functional polymeric
nanostructures patterned bottom-up by
colloidal lithography and initiated chemical
vapor deposition (iCVD)*
Nathan J.Trujillo, Sal Baxamusa, and Karen K. Gleason
Adapted from work originally published in Chemistry of Materials (2009),
29 (4) and Mater. Res. Soc. Symp. Proc. (2009), 1134-BBO8-27
*
3.1. Abstract
Colloidal lithography,
a popular inexpensive alternative
lithography, uses two-dimensional
self-assembled
to conventional
monolayer arrays of colloidal
nanoparticles as a lithographic template. Combined with initiated chemical vapor
deposition (iCVD), which offers unprecedented opportunity for producing grafted
polymeric layers, this work demonstrates a generic "bottom-up" process as an
inexpensive, simple, and environmentally friendly technique for creating robust wellordered arrays of functional patterned polymeric nanostructures up to 500 nm in height.
These grafted "nanobowl" patterns were produced for a broad material set of functional
organic, fluorinated, and silicon containing polymers. These polymers fully retain the
organic functionality of their monomeric precursors, are free of wetting defects, and are
robustly tethered to the underlying substrate as shown by their ability to withstand
aggressive solvent. Using this method we patterned a novel low dielectric constant
polymer down to 25 nm without the need for environmentally harmful solvents.
Furthermore, using capillary force lithography, we created topographical templates for
large-scale orientation of the nanoparticle assembly. This "top-down" approach reduces
the defect density of the bottom-up assembly and creates multi-scale functional
polymeric patterns without the need for expensive lithography tools.
3.2. Introduction
Materials patterning through non-conventional lithography can reduce the cost of
patterning fine structures when compared to traditional nanofabrication techniques such
as photolithography.! The current state-of-the-art in lithography couples 193 nm light
with immersion lithography and allows for patterning of sub-45 nm features.2 These
advanced developments require very costly instrumentation, and have difficulty
providing throughput commensurate industrial demands. 3 Nanosphere lithography has
emerged as a simple, convenient, low-cost method for creating large 2-D arrays of
nanostructures.4 These are proven techniques which can also be used to fabricate
complex opalescent 3-D photonic structures with both well-defined or tunable photonic
bandgaps.5- 7 Monodisperse colloidal particles can self-assemble into 2-D hexagonal
arrays when deposited onto various substrates. By controlling the drying process, solution
cast colloidal particles can self-assemble into a hexagonally closed packed monolayer.
Several strategies for creating centimeter-scale monolayers using commercially available
latex spheres have been described.8,9
The resulting void array in the particle interstices has been used as a patterning
mask for over 25 years.1 0 Evaporation and sputtering into these interstices have been used
to produce very thin films (< 30 nm) of metals and inorganic oxides. Their 2-D patterns
result from a line-of- site deposition of thin nano-dots, which may coalesce to form a
honeycomb pattern of thin lines. These structures have been used to pattern carbon
nanotube growth,
ZnO nanorods,
nickel and gold. 13,14
The desire to pattern functional polymers with colloidal templates provides
unique challenges. For example, a common approach for producing 2-D arrays of
functional polymers or inorganic oxides uses UV curable prepolymer,4 " sol-gel,4 ' 6 , 7 or
electrolyte 4' 17 ,18 precursors. The notable drawbacks to these liquid phase techniques
include through-pore defects from template deformation, concentration effects on
morphology,
template shifting, and incomplete infiltration resulting from surface
tension effects.19 Solution based processing can also be time consuming; requiring
anywhere between 12 hours to 3 days for precursors to polymerize.
7,20,21
'2,1Furthermore,
non-wetting adds additional difficulty when trying to produce patterns of homogeneous
structures from low-surface-energy liquid phase precursors, such as fluoropolymers. This
challenge is typically overcome by creating a heterogeneous structure, which consists of
an inorganic hydrophilic pattern which is subsequently modified with fluoroalkylsilane.16
Vapor phase polymerization processes avoid the difficulties resulting from
surface tension and non-wetting effects. Polymerization through PECVD has been
successful in creating homogeneous arrays of fluorocarbon nano-dots and nano-rings.
22
Figure 3-la contains a graphical representation of these structures. The polymer nanodots, ~ 25 nm tall, are situated directly under the particle interstices, which is analogous
to the line-of-site deposition observed in thermal evaporation. Highly mobile polymer
fragments may also form nano-rings under the spheres.22 An alternative 2-D patterning
process creates functional polymeric nanodomes. A colloidal template, assembled over a
polymer film deposited by PECVD, acts as an etch mask for reactive ion etch of the
underlying polymer. Nanopatterns of p(acrylic acid) 23 and PEG24 domes, over 200 nm
tall, have been created from this "top down" patterning. A major limitation of this method
is that the reactive ion etch can destroy delicate polymer functionality. Furthermore,
PECVD, a workhorse for the semiconductor industry, is a high energy process which can
destroy organic moieties through unwanted side reactions.
25-28
The large surface area
make the general formulation of 2-D patterns produced from solution or plasma
polymerization attractive for various applications which require functional nanostructures
such as catalysts, sensors, nanoreactors, antifouling surfaces, nanoactuators, and
photovoltaics. Notable disadvantages such as poor functional group retention, lack of
adhesion between the polymer and substrate, structural inhomogeneity, time-consuming
synthesis, non-wetting issues, and the negative environmental impact associated with
template removal, would preclude their wide-scale implementation in device fabrication.
.......
..........
......
...
..........................
::::..::
.......... .....................
..
....................
...
(a)
(b)-r
r
Figure 3-1: Schematic of thin dot and ring patterns which form from 2-D colloidal
patterning of PECVD polymer (a). The dotted circles represent the colloid template of
radius 'r'. The polymer feature height, h, is typically much smaller than 'r' (h << r).
iCVD films can produce truly hemispherical "bowl" structures from functional polymers.
These structures can either be spaced apart (b) if the film thickness is less than the
particle radius (h < r) or directly neighboring (c) if h - r.
Initiated chemical vapor deposition (iCVD) , is a solvent-free process 29,30 for
depositing thin polymer films, which requires much lower energy density for deposition
when compared to PECVD (0.02-0.12 W/cm2
29
versus 0.13-2.1 W/cm2
30,31),
allows for
100% retention of delicate functional groups, 30 and to date has been used to create thin
films from over 50 different functional precursors. Unlike PECVD mechanisms, iCVD
polymerization
is
well
understood
and
most
resembles
closely
free-radical
polymerization in solution.29 Moreover, in contrast to the dot and ring patterns produced
by PECVD, iCVD offers the ability to produce tall, > 250 nm, hemispherical "bowl"
structures from functional polymers, which can either be spaced apart (Fig 3-lb) or
adjoining (Fig. 3-1c). Compared to solution polymerization, iCVD offers reduced
polymer deposition time and avoids wetting effects, giving us the ability to produce
homogeneous polymeric films for pattern synthesis from high and low-surface-energy
precursors.
Because iCVD is a surface controlled process
opportunity for producing adherent patterned polymer films.
it affords unprecedented
30
Vinyl groups covalently
anchored to a surface can react with the initiating species by the same free radical
mechanism responsible for polymerization of vinyl monomers, allowing propagation to
proceed from the surface-bound radical. These grafting sites improve the adhesion for
both the directly bound polymer chains, as well as the subsequently deposited chains
which become entangled in the grafted layer or branch out from the grafted chains. The
ability to produce films with adhesion contrast is important to the novel patterning
technique we describe, as patterns can be developed in an environmentally benign
solvent. We employed the principle of colloidal lithography coupled with iCVD and
grafting to create a generalized process for "bottom-up" patterning functional polymers.
The excellent interfacial properties maximize the durability and reliability of these
functional patterns for device applications. 33 The methods we present in this report are
quick, simple, and generic; they can be extended to create robust patterns of grafted
functional nanostructures from any iCVD polymer without the need for environmentally
harmful solvents.
Finally, we employed capillary force lithography as a top-down approach for
assisting the bottom-up assembly to create spatially addressable features that are
hierarchically patterned. These are attractive for a variety of applications where spatial
registration of functional patterning patterns is desired.
3.3. Experimental Section
Preparation of Colloidal Monolayer: All chemicals were used as received without
further purification. 4" p-type silicon wafers (Waferworld) were cleaned for 5 minutes
2
with capacitive oxygen plasma (13.56 MHz, 100 W/cm , 100 mTorr). A solution of
monodisperse poly-styrene nanoparticles, 2.5% wt. (1 pm, 200 nm, 80 nm nominal
diameter, Polysciences) in water, was mixed 1:1 with a surfactant solution (Triton X100:methanol/1:400 volume) (Fischer Scientific),34 cast onto the plasma cleaned wafer in
discrete 2.0 ptL droplets, and allowed to dry under ambient conditions for 20 minutes. To
remove any residual water, the samples were then placed into a nitrogen purged vacuum
oven (VWR, 1400E) which was maintained at 60'C and -15" Hg gauge pressure. After 3
minutes, the nitrogen
flow was stopped
and the samples were
exposed to
tricholorvinylsilane (Aldrich, 98%) vapor at -30 in. Hg gauge pressure for 6 minutes.
iCVDfilm grafting: The custom built iCVD vacuum reactor configuration has previously
been detailed.
32
iCVD deposition conditions were adopted from previously reported
work for n-butyl acrylate (BA, Aldrich, 99%),32 hydroxyethyl methacrylate (HEMA,
Aldrich, 99%),
pentafluorophenyl
1H,1H,2H,2H-perfluorodecyl acrylate (PFDA, Aldrich, 97%),36 and
methacrylate
(PFM,
Monomer-Polymer,
95%).37
Tetravinyltetramethylcylcotetrasiloxane (V4D4, Gelest) monomer, heated to 90"C, and
tertbutyl peroxide (Aldrich, 98%) initiator, at room temperature, were delivered into the
reactor at 1.0 sccm and 0.5 sccm, respectively. The reactor pressure, substrate
temperature, and filament temperature were maintained at 350 mTorr, 50'C, and 300*C,
respectively. For each polymer, three samples were simultaneously coated via iCVD: 1)
colloid template on silane treated substrate 2) colloid template on hydroxylated substrate
3) blank silicon substrate for measuring film thickness in situ by laser interferometry. To
keep from over-coating the template all V4D4 depositions were terminated after a film
thickness, equal to the radius of the template, had been deposited.
Template Removal: Patterns produced from linear polymers were ultrasonicated by a 70
W ultrasonic cleaner, in 30 mL of THF (Aldrich, >99%) for 10 minutes, to remove the
colloidal template. The solvent was then replaced with fresh THF and the samples were
left to soak in the solvent overnight, for at least 8 hours. The V4D4 samples were
ultrasonicated in 30 mL of IPA (Aldrich, >99%) for 1 hour and subsequently dried under
nitrogen.
PFM Functionalization: PFM patterns were functionalized with fluorescein-5thiosemicarbazide (Molecular Probes) for 30 minutes using techniques described
elsewhere. 37 To remove any unreacted ligands, the functionalized patterns were triple
washed by shaking with 30 mL of ethanol in a sealed glass jar.
Multi-scale Patterning: A topographical template was created for the nanoparticle
assembly using capillary force lithography3 8 A 1.5% wt. solution of polystyrene (MWn =
45,800, Aldrich), dissolved in toluene, was spin-coated onto a plasma-cleaned silicon
wafer, to form a 300 nm thick film. A pre-patterned PDMS mold, created from a
polyurethane master, was placed onto the polystyrene film and pressed at 150'C, for 2.5
hours. This forced the polystyrene to be siphoned into the grooves of the mold (Scheme
3-la/lb). The pressed assembly was cooled at room temperature for one hour, to allow
the polystyrene to solidify; the mold was subsequently removed. The patterned silicon
substrate was then exposed to oxygen plasma for 1 minute. This etched away any
polystyrene that remained in the grooves. The colloidal nanoparticles were deposited into
the patterned grooves (Scheme 3-1c) and the grafted iCVD polymers were patterned,
according to the methods outlined above. The lift-off step removed the patterned grooves
as well as the nanoparticle assembly within the grooves, revealing hierarchal patterns of
grafted iCVD polymer. Pre-patterned low crosslink density PDMS stamps were used for
micro contact printing (pCP) the colloidal templates using previously published
procedures. 39
Film Characterization: The iCVD film composition was elucidated by transmission
mode FT-IR spectroscopy (Nicolet Nexus 870 ESP) using a DTGS-KBr detector. Spectra
were obtained through the patterned samples over the range of 400 cm-1- 4000 cm 4 at 4
cm- 1 resolution averaged over 64 scans, and baseline corrected. Contact angle
measurements were performed with a contact angle goniometer with automatic dispenser
(Rame'-Hart Model 500) using 2.5 pL water droplets.
Nanostructure characterization: The patterned samples were sputter coated with 5 nm of
gold and SEM images were obtained using a JEOL JSM 6060 with 5 kV acceleration
voltage. Sub- 100 nm patterns were imaged using a JEOL 6320FV Field-Emission High-
......
........
...
..........
resolution SEM at 2 kV acceleration voltage. Fluorescence microscope images were
obtained at 50x magnification using a Zeiss Axiovert 200 inverted microscope with FITC
illumination. Atomic force microscope images were generated using a scanning Probe
microscope (Digital Instruments, Dimension 3100) in tapping mode with a 1.0 Hz scan
rate. Film thicknesses were measured using spectroscopic ellipsometry (J.A. Woollam M2000S). Data was collected at 68' incidence angle for 190 wavelengths between 315nm
and 718 nm. The data was fit to a Cauchy-Urbach model from which the thickness values
were extracted.
(b)
(a)
T,P
PDMS Mold
PS Melt
Substrate
Solidify Polymer,
Remove Mold
(TopView)
CDeposit
Colloidal SAM
(Side View)
Scheme 3-1: A generic process scheme for creating a topographical template used for
producing hierarchical patterns of polymeric
nanostructures, by capillary force
lithography. A patterned PDMS mold is pressed onto a polystyrene melt (a/b). After
cooling, the mold is removed. A SAM of colloidal particles is deposited into the grooves
(c). This hierarchical template is used for patterning the iCVD polymers, according to
Figure 3-1.
3.4. Results and Discussion
The process used here for creating polymer patterns from 2-D colloidal templates
is shown in Figure 3-2. A silicon substrate was treated with oxygen plasma both to
remove any organic impurities
40
and to increase the surface hydroxyl concentration.4 1
Increasing the hydroxyl concentration not only provides more surface sites for
subsequent silyation chemistry, but creates a hydrophilic surface which is critical for
forming a monolayer of the colloidal particles.4 Monodisperse polystyrene nanoparticles
were cast onto the plasma treated wafer in discrete droplets, and allowed to dry under
ambient conditions (Fig. 3-2a). The samples were then loaded into a vacuum oven and
exposed to tricholorvinylsilane vapor. A monolayer of vinyl-silane coupling agent was
covalently bound onto the silicon substrate through hydrolysis of the chlorine moieties by
surface hydroxyls.
42
This occurs only in the exposed regions of the substrate through the
particle interstices (Fig. 3-2b), thus providing an anchor point for grafting iCVD polymer.
A blanket polymer film was then deposited onto the substrate via iCVD (Fig. 3-2c), with
only the polymer deposited in the interstices undergoing grafting through the surface
vinyl groups. The grafted films were subsequently placed in an ultrasonic bath and rinsed
in THF to lift off the polystyrene particles and any non-grafted polymer. This step
revealed largely ordered honeycomb-like arrays of polymer covalently bound to the
substrate through free radical polymerization about the substrate-tethered vinyl group
(Fig. 3-2d).
...................
........
............
............................
......................
OH
...............
(b)
(d)
Figure 3-2: A generic process scheme for producing patterned polymeric nanostructures
using colloidal lithography. A hydroxylated substrate which has been treated with an
oxygen plasma serves as a hydrophilic base for depositing a 2-D assembly of colloidal
nanoparticles (a). The masked sample is then treated with a vapor phase silane coupling
agent which covalently attaches vinyl groups to the substrate in the exposed regions of the
colloidal mask (b). This acts as an adhesion promoter to graft the functional iCVD
polymer which is subsequently deposited (c). The grafted film is sonicated in solvent to
remove the colloidal template and any ungrafted polymer. This reveals an array of bowl-
shaped nanostructures patterned in a hexagonal arrangement (d).
To demonstrate the versatility of this process, functional homopolymer patterns
were produced from five different monomer precursors. Figure 3-3 depicts the FT-IR
spectra and the molecular structure of the various iCVD films which were successfully
patterned with 2-D colloidal templates.
The biocompatible polymer pBA has a low glass transition temperature (-55"C)
43
that makes it attractive as a non-crystallizable segment in shape memory polymers. '4
32
Alkyl acrylates have a characteristic carbonyl stretch between 1732 and 1736 cm-1. This
peak remains unchanged from the BA monomeric precursor (Fig. 3-3a) and iCVD
polymer film (Figure 3-3b). Furthermore, the pBA polymer can be identified through the
double band at 950 cm-1,32 thereby indicating the preservation of the original
functionality, and by the absence of the vinyl peaks present in the monomer precursor
between 1630 cm- and 1650 cm-land also at 1410 cm-1.
The iCVD pHEMA behaves as a hydrogel and can absorb high water content and
swell in the absence of crosslinker.35 The C=O stretching modes between 1750-1690 cmI, C-O stretching (1300-1200 cm-1), and C-H bending at 1500-1350 cm-1 appear in both
the spectra obtained for the monomer precursor (Fig. 3-3c) and as-deposited film (Fig. 33d). There is also a broad peak centered at 3450 cm-1 (not shown) which is present in both
monomer and polymer spectra and signifies that the functional hydroxyl group is retained
after polymerization. This is consistent with previously reported results,3 5 which indicate
that the entire functional pendant hydroxyethyl functional group is retained in the iCVD
polymer. By preserving this delicate functionality, iCVD preserves the ability to create
patterned, responsive surfaces.
The iCVD pPFDA is a low surface energy ( 9.3 mN/m) 36 fluorocarbon film which
imparts superhydrophobic behavior to various surfaces. PFDA contains two sharp peaks
at 1207 and 1246 cm-1 corresponding to the -CF 2 - symmetric and asymmetric stretching
36
modes as well as a third peak at 1153 cm' which represents the -CF 2-CF 3 end group.
The strong presence of these peaks in both the monomer (Fig. 3-3e) and polymer (Fig. 3-
3f) spectra indicates that the iCVD film retains the original fluorine functionality present
in the precursor.
The iCVD pPFM is another functional fluoropolymer, which is useful for
immobilizing biomolecules through a single-step nucleophilic substitution of the
pentafluorophenyl moiety by a primary amine.37 The intense peak at 1523 cm-1 is
characteristic of the fluorine substituted phenyl moiety and is present in both the
monomer precursor (Fig. 3-3g) and the iCVD polymer (Fig. 3-3h). Peaks at 1069 cmand 1000 cm-1, corresponding to the C-O ester bond and C-F bonds, respectively, are also
found in both the polymer and monomer spectra. The low energy input for free radical
polymerization and absence of energetic charged species preserves the delicate ester side
group, which can be damaged in alternative vapor deposition processe.
45
Low dielectric constant, k, polymers have been introduced into the interconnect
structures of integrated circuit to improve device performance by reducing cross talk and
power consumption associated with parasitic capacitance losses through the intralevel
connections.46 Cyclic organosilicon polymers are a class of low-k materials identified to
facilitate integration into the interconnect structure of integrated circuits because of their
attractive electrical, mechanical and thermal properties. 47 V4D4, is a cyclic siloxane, with
a structure analogous to commercially available low-k precursors and with a "puckered"
ring that allows for the formation of a 3D bonding network through vinyl crosslinks.
Figure 3-3 contains FT-IR spectrum from both the monomer precursor (i) and the asdeposited dense iCVD pV4D4 film (j). Film deposition through free-radical vinyl
polymerization is apparent by the reduction of the vinyl absorption bands at 960 cm',
1410 cm1, 1600 cm', and the subsequent formation of methylene bridges at 2900 cm~
'(not shown).48 The methyl groups bound to Si appear between 1230 cm-1-1280 cm-1. The
100
region between 950 cm' and 1200 cm-1 corresponds to Si-O skeleton stretching. This
region corresponds to three different substructures (Si-O bonding environments):
suboxide with bond angle <1440 and peak around 1020 cm-1, network (bond angle -144
0)
at 1060 cm', and cage structure with bond angle ~150" which peaks at about 1150 cm-
.49 The broadening of this peak towards higher wavenumbers indicates that the open
siloxane structure of the monomer was preserved after polymerization.
The results shown in Figure 3-3 directly demonstrate the benefits of iCVD, which
include deposition of material of limited or no solubility such as fluorocarbon films and
crosslinked layers. The absence of wetting effects allowed us to produce patterns with
consistent morphology for a variety of functional materials. Deposition rates of all the
materials fall in the 30 to 200 nm/min range, which means the polymerization process
takes a few minutes, instead of several hours as in solution polymerization.
7,20,21
Furthermore, because no solvent is required for polymerization, the template deformation
and shifting associated with solution processing is avoided.
101
Utility: Low temperature martensitic
phase for biocompatable shape
memory polymers
O
Utility: High surface energy hydrogel
polymer whose swelling can be
systematically controlled
OH
O
<
Utility: Hydrophobic low surface
energy polymer
0
CF2) 7 CF3
O
Utility: Functional polymer for binding
biological ligands.
0
F
F
F
Utility: Low dielectric constant
polymer for integrated circuits
O-
si-0
0.0Si-O
1900
1000
1600
1300
wavenumber (cm- 1)
Figure 3-3: FT-IR spectra for (a) butyl acrylate monomer, (b) corresponding iCVD film,
(c) HEMA monomer, (d) corresponding iCVD film, (e) PFDA monomer, (f) corresponding
iCVD film, (g) PFM monomer, (h) corresponding iCVD film, (i) V4D4 monomer, (j)
corresponding iCVD film. The grey bar highlights the position of the vinyl C=C
absorption. The noted reduction in this peak in the iCVD polymer is consistent with free-
102
radical polymerization.
The functional similarity between
monomers
and their
corresponding iCVD film is highlighted with asterisks (*), and suggests the preservation
of functional groups in the polymer films.
Figure 3-4 contains SEM images of the grafted functional polymer patterns
obtained from linear polymer precursors, using 1 tm polystyrene spheres as a template.
Figure 3-4a reveals the pBA honeycomb pattern that was produced after the colloidal
template and ungrafted homopolymer were removed with THF. The conformal nature of
the iCVD process
coupled with the "bottom-up" growth mechanism of the free radical
polymerization allows the colloidal assembly to act as a template allowing the grafted BA
pattern to preserve the hemispherical geometry of the colloidal template. This is in
contrast to the vapor phase sputter processes, which have utilized the particle assembly as
a shadow mask for "top down" deposition techniques for producing thin patterned dots.
Figure 3-4b shows a large area (-25,000 um2) of the grafted 2-D honeycomb bowl
pattern produced from PFM. These patterns were functionalized with fluorescein-5thiosemicarbazide. The amine functionality allows this fluorescent molecule to become
immobilized
on
the
patterned
pPFM
substructure
upon
reacting
with
the
pentafluorophenyl ester. After functionalization the sample was rinsed in ethanol several
times and visualized under FITC illumination (Figure 3-4b inset). The fluorescent pattern
indicates that the fluorescein-5-thiosemicarbazide was indeed immobilized, and therefore
that the functionality of the PFM precursor was realized in the patterned polymer film.
These large surface-area functionalizable patterns are robustly tethered to the substrate
103
and can serve as a robust polymeric substructure for immobilizing proteins, peptides, and
other biological ligands. 50
Very well-ordered arrays of grafted pHEMA hydrogel patterns were also obtained
(Fig. 3-4c). iCVD HEMA homopolymers can swell up to 55% upon uptake of water,35
making these types of nanostructures useful for creating responsive surfaces for potential
sensing,1
actuation, 52 and photonics 7 applications. The patterned hydrogel film
demonstrated significant contact angle hysteresis and the observed ultimate receding
water contact-angle, Figure 3-3c inset, was 15" (± 20). These results are consistent with
the previously reported water contact angle of 170 and dramatic hysteresis behavior for
iCVD pHEMA which results from surface-state equilibration of the polymer with the
wetting medium.35
Fluoropolymer films, besides offering excellent water repellency, have found
applications in MEMS devices 5 3 and amphiphilic non-fouling surfaces.5 4 Patterning these
films by conventional lithographic methods requires that the film undergo a reactive ion
etch, which can damage the delicate fluorine functionalities5 5 and greatly impact the
properties of the patterned films. Figure 3-4d shows a patterned film of grafted PFDA.
The inset demonstrates the water repellence of the patterns, with a contact angle of 1300
(
50),
which is consistent with values reported for iCVD pPFDA.
AFM measurements
indicate that the film thickness was 140 nm, which is much less than the radius of the
template. As illustrated in Figure 3- lb, this causes the feature width to appear larger than
those deposited from the other polymers depicted in Figure 3-4. These fluoropolymer
"nano-bowls" represent a significant contrast to fluoropolymer "nano-dots" and "nanorings" which have been produced by colloid lithography and PECVD
and are
potentially useful for a variety of applications such as a template for assisting the self
104
.......................
.....
-X- ---..................
.............................
- -...................
.
. .
.
.
....
...................
. ..................................
assembly and aggregation of functional nanoparticless657 to create structures with wellcontrolled hybrid functionalities.
a
b
BAPFM
C
d
PFDA
Figure 3-4: SEM images for grafted functional "nanobowls", produced from 1 Pm
diameter spheres, after the colloid template had been removed. p(butyl acrylate) patterns
(a) were very well ordered . A large continuous pattern of pPFM (b) can create a reactive
surface. These patterns contain a reactive pentafluorophenyl ester which was used to
immobilize an amine-containing fluorescent ligand through nucleophilic addition. The
inset contains a fluorescence microscope image of the fluorescent patterns. Hydrogel
patterns from pHEMA (c) are incredibly hydrophilic (inset) unlike those produced from
low surface-energy pPFDA (d) which are water repellent (inset). All iCVD films were
105
devoid of wetting defects, such as those which would have given rise to island type pattern
growth.
The AFM image and accompanying line scan in Figure 3-5 show that the particles
were successfully removed by ultra sonication in THF. Furthermore, the geometry of the
polymer wells, with feature heights as great as 500 nm, preserves the hemispherical HCP
lattice generated by the self-assembled monolayer template. The dotted white curve
overlay is a theoretical representation of the 1 pim diameter hemispherical template,
which has been scaled for comparison with the line scan. The theoretical line very closely
traces the actual geometry of the polymer "bowl", and deviations in the fidelity can be
attributed in part to convolution from the AFM tip. To our knowledge, these are the
tallest set of organic polymer features which have been reported for vapor phase
patterning by 2-D nanosphere lithography.
106
.. ..
....
...
.. . ......
......................
:
................
W
..
..........................
.............
.....
Figure 3-5: Typical AFM image and line scan for patterned "nanobowls" from 1 sm
diameter colloidal template, p(butyl acrylate) pictured. The tallest features are about 500
nm in height. The line scan shows how the honeycomb polymer pattern regularly
preserves the hemispherical geometry from the colloidal template, which is theoretically
represented in the dotted white curve which appears as an elliptical overlay on the graph
since the horizontal and vertical scales are in ratio of 4:1. The features traced are -300 nm
in height.
As compared to adjacent areas of unpatterned substrates, the interstices display a
larger grafted thickness. Thus, a greater degree of entanglement, higher crosslinking
density, and/or increased molecular weight are anticipated in the nanopatterned regions.
107
Because of small overall volumes, it is experimentally difficult to distinguish between
these possibilities. Any changes in grafted polymeric structure would reflect the impact
that the geometry of the confined region, within the interstices, has on local growth
conditions. While patterning would not be expected to alter the relative arrival rates of
the monomer and the initiator radicals, the potential for multiple collisions with the walls
within the interstices would be expected to lower the relative probability of escape of the
monomer, which has the higher sticking coefficient per collision. 58 Creating a monomer
rich environment would enhance the molecular weight of linear chains 59 as well as
increase the probability of branching reactions,60 such as chain transfer to the polymer
backbones.
It is crucial to emphasize the importance of the silyation step in the patterning
process described in Figure 3-2; without pre-treating the wafer with the adhesion
promoter trichlorovinylsilane, the polymer will be removed from the surface after the
sonication step. The patterns in Figure 3-4 were imaged after 10 minutes of sonication in
THF and additional overnight soaking (> 8 hours total); however, the linear
homopolymers of Figure 3-4 are not crosslinked and are extremely soluble in common
solvents. The use of adhesion promoter prevents the patterned polymer from dissolving
into the solvating media, allowing creation of robust patterns with features as small as
150 nm in width (Fig. 3-6a), whereas the patterns produced on surface without adhesion
promoter were incapable of withstanding a gentle 5 second rinse in THF (Fig. 3-6b).
Therefore, the covalent attachment between the polymer and the substrate is a necessary
step and provides a robust interface that renders the patterns insoluble in aggressive
solvents.
108
Figure 3-6: The grafted polymer patterns produced from 1 sm particles ( p(butyl
acrylate) shown) typically generate features 150 nm in width (a). Because of the vinyl
pretreatment these patterns are robust and withstand several hours in THF. The silyation
step is necessary to covalently attach the iCVD polymer to the substrate. Without this step
the polymer is easily washed away during the template lift-off, leaving behind a clean
substrate (b). The insets depict the corresponding substrate functionality prior to
patterning.
Because the adhesion promoter acts only on the iCVD polymer, the adhesion
contrast between polymer/substrate and polymer/template interfaces allows for patterns
to be generated without having to dissolve the colloidal template. Therefore, the use of an
aggressive solvent, many of which are environmentally harmful, is not a requirement for
producing these robust structures, as the colloidal template can be removed by simple
109
agitation in a mild, environmentally-friendly media. To demonstrate this concept we
produced patterns from pV4D4 which were developed in isopropyl alcohol (IPA).
Neither the pV4D4 films, which are highly crosslinked, nor the polystyrene template are
soluble in IPA. Furthermore, IPA is biodegradable, not likely to bioconcentrate, has low
potential to affect organisms, and is an environmentally-friendly substitute for common
solvents used in lithography such as tetramethylammonium hydroxide61 or hydrofluoric
4,62-64
The use of a mild media is also an improvement upon more typical techniques
acid.'2-
for template removal by calcination,
'17'65'66
as such high temperatures are incompatible
with functional group retention in polymers. We created high-resolution features with
this process by using three different particle sizes (1 pim, 200 nm, and 80 nm) as the
patterning template. Figure 3-7 contains SEM images for V4D4 patterns developed in an
ultrasonic bath of IPA for 1 hr. The patterns produced with 1 prm particles (Fig. 3-7a),
200 nm particles (Fig. 3-7b), and 80 nm particles (Fig. 3-7c) have an identical
nanostructure to those shown in Figure 3-4. The physical agitation resulting from the
ultrasonic bath jostles the template loose from the crosslinked polymer film, leaving
behind the pattern of hemispherical depressions, thus allowing the patterns to develop
across several length scales. In order to facilitate the template removal, the film thickness
was controlled to minimize the over-coating on the template. We achieved feature
dimensions as small as 25 nm in width for patterns produced from 80 nm particles using
IPA as the developer. The ability to create robust low-k materials using a low
energy/waste process, such as iCVD, and substitute harmful solvents for patterning sub50 nm features is a step towards EHS-focused dielectric processing to meet the newly
instituted ITRS roadmap requirements for environmentally-friendly semiconductor
110
manufacturing 67 and to reduce costs when compared to more conventional PECVD and
spin-on processes.
pm
a2
I
Figure 3-7: SEM images for patterned V4D4 dielectric polymer using (a) 1 sm, (b) 200
nm and (c) 80 nm diameter templates. The template was removed in an ultrasonic bath of
an environmentally-friendly solvent, isopropyl alcohol. The smallest obtainable features
were 25 nm in width, obtained from 80 nm particles.
The above experimental procedure created regions of monolayer coverage with an
area greater than 0.3 cm 2 . This method was not optimal for creating the largest areal
monolayer coverage as Langmuir-Blodgett type techniques have been described for
depositing a continuous monolayer of colloidal particles over areas of several cm 2 8'9
Practical implementation of these robust functional polymer requires large scale
order; the self-assembly must contain few point and line defects. By providing a
111
topographically patterned template, which can also be produced via non-conventional
lithography or by electrode assisted assembly,68 one could achieve long range order
within a nano-patterned regime
69.
Therefore, precisely defined large-scale features can
drive rational design at the nanoscale
69(
since the colloidal crystal template defines the
lowest level for hierarchical polymer patterns). Templated self-assembly can produce
spatially addressable nano-features with low line-edge roughness69 for various device
applications. We employed capillary force lithography techniques to form hierarchically
patterned iCVD nanostructures, without the need for expensive lithography equipment.
Combining processes for large scale low-defect self assembly with our generic
process for creating robust functional patterns is a rout towards hierarchical structures
logically designed for widescale device fabrication and implementation for a variety of
applications.
The methods we present in this report are generic, and can be extended to create
addressable patterns of grafted functional nanostructures from any iCVD polymer.
Preliminary attempts at hierarchical patterning used microcontact printing (pCP)
for creating spatially addressable features. 39 The polystyrene beads were arranged in an
HCP pattern that was reminiscent of the line features that were pre-patterned in the
PDMS stamp. Figure 3-8a and 3-8b respectively show an AFM and SEM image of
p(V4D4) hierarchically patterned through 1 pm polystyrene beads. These images
demonstrate high line-edge-roughness and non-specific placement of stray beads in
between the line patterns of the p(V4D4) film after template liftoff. Although,
hierarchical patterning was achieved, these patterns were not sufficiently well-defined
over large areas and were far from optimal.
112
..............
11
..........
11
................
....
11
............
....
..........
...
..
..
......
......
..
..................
.
.......
Figure 3-8: Hierarchical patterns were preliminarily generated by micro contact printing
the colloidal template. AFM (a) and SEM (b) images of hierarchically patterned V4D4
show high line-edge-roughness and stray beads within the unpatterned region.
Figure 3-9a is an optical micrograph that depicts a set of polystyrene lines,
patterned by capillary force lithography. The PDMS mold contained sets of grooves of
varying width, with a 6 prm pitch. Therefore, the patterns transferred onto the polystyrene
were capable of confining a monolayer of six, close- packed 1 pm polystyrene particles
(Figure 3-9b). This hierarchical assembly was then used as a template for grafting iCVD
polymer. After the template was lifted off, hierarchically patterned, grafted iCVD
polymer was revealed.
These patterns contain two periodicities, at different length
scales. The first periodicity, corresponding to the larger length scale, is attributed to the
polystyrene template. The iCVD patterns are separated from one and other by a distance
equal to the width of the grooves (Figure 3-9c) in the PDMS mold, and, in contrast to
pCP, no stray beads were located within the unpatterned linewidths. The geometry of this
template is not limited to parallel grooves. Multiple geometries have been explored for 2-
113
D templated assembly, including circles and polygons.
56
The second periodicity, in the
iCVD polymer, is attributed to the colloidal template (Figure 3-9d). This is the smaller
length scale that gives rise to the nanostructure. This length scale can be easily tuned by
selecting colloidal particles of a different diameter.
Figure 3-9: Hierarchical patterns from grafted iCVD polymer were produced with
capillary force lithography. A polystyrene template (a) was used to template the colloidal
assembly (b). The iCVD polymers (pHEMA shown) are patterned at two length scales.
The large length scale corresponds to the polystyrene template (c). The smaller length
scale is attributed to the colloidal template (d).
114
3.5. Conclusions
We have presented a simple set of techniques to create large well-ordered
arrays of functional polymeric nanostructures which are covalently bound to the
substrate. These structures were templated by a 2-D assembly of a colloidal monolayer
and grafted onto the underlying substrate by a unique "bottom-up" approach. iCVD is the
enabling technology that allowed production of grafted micro- and nano- patterned
polymeric films. These films were produced by vinyl polymerization through the iCVD
process and preservation of the functional pendent groups was verified by FT-IR
spectroscopy, contact angle measurement, and chemical functionalization. Patterns were
generated for a broad material set of functional iCVD films, including organic polymers
(pBA, pHEMA), fluoropolymers (pPFDA, pPFM), and organosilicones (pV4D4). The
properties of these materials range from hydrophilic (pHEMA) to hydrophobic (pPFDA);
from soluble linear polymers (pBA) to heavily crosslinked networks (pV4D4); and to
films with highly reactive pendent groups which are readily biofunctionalized (pPFM).
Wetting defects were absent for all iCVD produced structures, including fluoropolymers.
All patterns survived long exposure to an aggressive solvent and AFM imaging shows
that the patterned films produce a "bowl" structure which matches the hemispherical
geometry of the colloidal template, with features up to 500 nm in height. The lack of
adhesion between the grafted films and the colloid template allows the patterns to be
produced in an environmentally benign media, as demonstrated by the ability to produce
high resolution patterns of crosslinked dielectric polymer across a variety of length
scales, down to 25 nm. We employed capillary force lithography as a top-down approach
for assisting the bottom-up assembly. This process is generic and is an inexpensive way
to pattern any iCVD polymer to create high surface-area honeycomb patterns that are
115
hierarchically patterned, which is attractive for a variety of applications where spatial
registration of functional patterns is desired.
3.6. Acknowledgements
The authors acknowledge the support of the NSF/SRC Engineering Research
Center for Environmentally Benign Semiconductor Manufacturing as well as the support
of the National Defense Science and Engineering Graduate Fellowship. This work made
use of shared electron microscopy facility in the MIT Center for Materials Science and
Engineering (CMSE).We would like to thank Sung Gap Im for providing the PDMS
molds.
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118
Chapter 4
Oxidative chemical vapor deposition (oCVD)
of patterned and functional grafted
conducting polymer nanostructures*
Nathan J.Trujillo*, Miles Barr", Sung Gap In't, and Karen K. Gleason
Published in Journal of Materials Chemistry 2010, 20, 3968- 3972
t Contributed equally to this work
*
119
4.1. Abstract
We present a simple one-step process to simultaneously create patterned and
amine functionalized biocompatible conducting polymer nanostructures, using grafting
reactions between oxidative chemical vapor deposition (oCVD) PEDOT conducting
polymers and amine
functionalized
polystyrene (PS)
colloidal
templates.
The
functionality of the colloidal template is directly transferred to the surface of the grafted
PEDOT, which is patterned as nanobowls, while preserving the advantageous electrical
properties of the bulk conducting polymer. This surface functionality affords the ability
to couple bioactive molecules or sensing elements for various applications, which we
demonstrate by immobilizing fluorescent ligands onto the PEDOT nanopatterns.
Nanoscale substructure is introduced into the patterned oCVD layer by replacing the
FeCl 3 oxidizing agent with CuCl 2.
120
4.2. Introduction
High-resolution functional polymer patterns have recently gained exposure from
their widespread applications in tissue engineering and biosensors, 1-4 anti-biofouling,5
microelectronics,6 optics,7 and MEMS.8 Micro- and nanopatterning of functional
polymeric materials enables precise definition of reactive chemical moieties that can be
used to selectively immobilize target molecules for a desired application. For example,
patterned bioactive molecules such as cell growth factors and matrix proteins induce
anisotropy in cardiac myocytes,9 which can increase their viability. Furthermore,
selectively patterned antibodies can facilitate spatially directed deposition of mammalian
cells for biosensor applications.' 0
It is no surprise that micro- and nanopatterned conducting polymers have been an
11 12
integral component in state-of-the art biosensors and various biomedical applications.
Conducting polymers, such as poly(3,4-ethylenedioxythiophene) (PEDOT), can provide a
biocompatible platform for interfacing biological systems with electronic devices.
These devices can convert biological signals into electronic signals, and vice versa.
Furthermore, the softness and flexibility of these organic materials closely mimic the
natural environment for tissue growth, and provide an innocuous alternative to inorganic
conductors. 13 For example, it has been shown that PEDOT does not induce a cytotoxic
response in heart tissue14 and demonstrates high cell viability when polymerized around
living neural cells.' 5 Moreover, a variety of counter ions can be incorporated into
PEDOT, providing avenues for ionically modulating cell-substrate interactions.14
It is known that functionalized conducting polymers with the attachment of
biomotifs, such as growth factors, enable even greater ability to control the adhesion and
growth of cells on surfaces. 16-18 However, complex synthesis routes are commonly
121
required for imparting functional groups onto commercially available conducting
polymer precursors.1 8-20 Alternatively, "grafting to" techniques have been used to impart
amine functionality to conducting polymer films. 16 ,21, 22 In addition to complex synthesis
routes, these techniques require surface activation with UV light or plasma discharge,
which can damage the underlying conducting polymer. Carboxylate functionalized oCVD
copolymers have directly been deposited,
23
but this approach has not yet been extended to
other functional groups, often because required monomers are not readily available.
Chemical vapor deposition (CVD) is compatible with CMOS processing and is
the most promising method to accommodate in vivo measurements using systems-onchip.
Within this framework, oxidative chemical vapor deposition (oCVD) can
conformally deposit thin, adherent coatings of PEDOT and other conducting polymers on
practically any substrate via a step-growth polymerization process.2 5 This process allows
for direct control over dopant concentration, work function, and conductivity by varying
substrate temperature;26 we have reported conductivities as high as 1000 S cm-1.27
Here, we present a novel process in which well-ordered conducting polymer
nanostructures are simultaneously patterned and functionalized by combining oCVD with
colloidal lithography. Colloidal lithography can reduce the costs and complexity when
compared to conventional lithographic techniques, and cost-effective biosensors that
28-30
utilize patterned structures from colloidal lithography have been demonstrated.
Moreover, it has been shown that the spatial confinement and regularity presented by
colloidal patterns can be useful for aligning cells for studying their interactions.3 1
Similar to our recently reported technique that uses colloidal lithography and
initiated chemical vapor deposition (iCVD) to pattern grafted non-conductive polymer
nanostructures , 32 we employ commercially available polystyrene (PS) beads to create
122
arrays of grafted conducting polymer nanobowls with large surface area. In both
techniques, substrate grafting is essential to successful patterning. However, in contrast to
the iCVD patterning technique, here we exploit the unique polymerization mechanism of
the oCVD process to directly transfer the functionality of the colloidal template to the
surface of the bulk conducting polymer patterns. Thus, a well-ordered interface with
specific functionality or bioactivity can be created by using surface-functionalized PS
beads, such as those containing amine, carboxylate, hydroxylate, sulfate, or protein
conjugation, while maintaining the advantageous properties of the underlying bulk
conducting polymer.
This process takes advantage of the unique properties of oCVD, which creates
PEDOT films that are covalently grafted to PS and other aromatic-containing surfaces by
the Kovacic mechanism. 33 In this process, a vaporized oxidant, such as FeCl 3 , forms
radical cations in the EDOT monomers and the benzene moieties on the PS chains. These
radical cations combine to form covalent bonds between the growing PEDOT film and
the PS substrate. This process generates a robust interface that prevents delamination
during patterning applications.3 3 Similarly, oCVD PEDOT films can be covalently
grafted to Si wafers by pre-treating the wafers with a linker material such as
trichlorovinyl silane (TCVS). During the oCVD process, the oxidant converts these
surface vinyl groups to radical cations, which combine with the EDOT to covalently
tether the PEDOT film onto the Si wafer.
4.3. Experimental
Preparation of Colloidal Monolayer: The procedure used to cast a monolayer of
colloidal particles has been detailed elsewhere. 32 Briefly, monodisperse 1 pm polystyrene
spheres, both non-functionalized or primary amine functionalized (Polysciences), were
123
diluted in a 1:1 ratio with a solution of methanol and Triton X- 100 and cast onto plasma
cleaned silicon wafers in discreet 2 pL droplets. To remove any residual water, the
samples were then placed into a nitrogen purged vacuum oven (VWR, 1400E) which was
maintained at 60 'C and -15 in. Hg gauge pressure. After 3 min the nitrogen flow was
stopped, and the samples were exposed to tricholorvinylsilane (Aldrich, 98%) vapor at 30 in. Hg gauge pressure for 6 min.
oCVD Film Grafting: Conducting polymer PEDOT films were deposited using a custom
built reactor that has been previously detailed.3 4 Low roughness PEDOT films were
deposited using FeCl 3 (Aldrich) as the oxidizing agent and nanoporous PEDOT films
were deposited using CuCl 2 (Aldrich) as the oxidizing agent using previously detailed
reaction conditions. 26,35 The substrate temperature was set at 85"C to help enhance the
film conductivity.
Template Removal: PEDOT patterns were ultrasonicated with a 70 W ultrasonic cleaner,
in 30 mL of THF (Aldrich, >99%) for 2 min, to completely remove the colloidal
template. The samples were subsequently dried under nitrogen for 10 seconds.
Pattern Functionalization: After the template had been removed, amine functionalized
PEDOT patterns were immersed for 4 hours in a 1 wt% solution of NHS-Fluorescent dye
(NHS-Fluorescein, 494 nm excitation wavelength, 521 nm emission wavelength, Pierce
Scientific) in DMSO. The samples were then triple rinsed with copious quantities of
DMSO to remove any unbound fluorescent ligands.
124
Film Characterization: The iCVD film composition was elucidated by transmission
mode FT-IR spectroscopy (Nicolet Nexus 870 ESP) using a DTGS-KBr detector. Spectra
were obtained through the patterned samples over the range of 400-4000 cm-1 at 4 cm-I
resolution averaged over 64 scans and baseline corrected. Three types of spectra were
obtained: as deposited PEDOT on a silicon wafer, non- functionalized colloidal template
cast onto a silicon substrate, and one in which the PS template was removed by rigorous
rinsing and ultrasonication (2 min) in THF.
Nanostructure Characterization: The patterned samples were sputter coated with 5 nm
of gold, and SEM images were obtained using a JEOL JSM 6060 with 5 kV acceleration
voltage. High resolution patterns were imaged using a FEI/Philips XL30 FEG ESEM
with a 5 kV acceleration voltage. Fluorescence microscope images were obtained at 50x
magnification using a Zeiss Axiovert 200 inverted microscope with FITC illumination.
The film conductivity was determined using a two-point probe measurement (Agilent)
with probe spacing of 3 mm on unpatterned PEDOT films; bulk resistivity values were
obtained across patterned regions.
4.4. Results and Discussion
Scheme 4-1 illustrates how this enhanced surface adhesion to both Si and PS is
utilized here for simultaneous patterning and functionalization of conducting PEDOT
films. Monodisperse PS beads are cast onto oxygen-plasma treated Si wafers and allowed
to dry under ambient conditions, forming a 2-D self-assembled hexagonal close-packed
(HCP) colloidal template. This patterned surface is then exposed to TCVS vapor, which
modifies the exposed area of the Si wafer by forming a monolayer of covalently bound
vinyl groups on the surface (Scheme 4-la). This occurs only in the exposed regions of the
125
substrate through the colloidal template and provides an anchor point for subsequent
grafting of oCVD conducting polymer. A blanket PEDOT conducting polymer film is
then deposited via oCVD, in which the substrate is exposed to EDOT monomer vapor
while oxidizing agent (FeCl 3 or CuCl 2 ) is simultaneously sublimed to the surface. The
substrate is maintained at elevated an elevated temperature (ca. 85'C) to maximize
PEDOT conductivity26 without destroying the underlying PS template. When the oCVD
process is applied to the colloidally patterned substrate, the resulting PEDOT film
conformally covers the PS beads and the coating infiltrates through the interstices to the
bottom of the HCP pattern. The oCVD PEDOT coating becomes covalently bound to the
surfaces of both the PS beads and the Si wafer (Scheme 4-lb). The non-grafted cores of
the PS beads are then dissolved out with tetrahydrofuran (THF) (Scheme 4-1c). Since the
PEDOT coating is grafted to the Si wafer, the solvent rinsing step does not delaminate the
patterned PEDOT film from the Si wafer. After the THF rinsing, the covalently bound PS
polymer chains remain on the PEDOT coating as a grafted capping shell.
126
........
......
......
....
..
..
....
.............
11
....
....
..
..
........
......
PS Beads
(a) Vinyl-Treated
.
......
..
... ....
.......
....
.. .. ....
[
0 0
I
A
iC
Silicon
Reombiation
Depotonation
Grafted
PEDOT0
H
o
PEDOT ==E*o
Pattern With
PS Surface
Layer
+
S
Grafted
(C)
o
o
o00
Fried
s
Cyst
o0
0
Scheme 4-1: PS beads are self-assembled on a vinyl-treated Si wafer to form a 2-D HCP
colloidal template (a). PEDOT is deposited via oCVD, conformally coating the void space
of the colloidal template with conducting polymer, which grafts to the surfaces of the PS
beads and the vinyl-treated wafer (b). The non-grafted cores of the PS template are
removed via dissolution and rigorous ultrasonication in THF, revealing well-ordered
PEDOT nanostructures with a grafted PS surface layer.
Figure 4-1 contains SEM images of the grafted PEDOT conducting-polymer
patterns obtained using the oCVD colloidal patterning scheme described above. The
conformal nature of the oCVD process coupled with the growth mechanism of the oCVD
polymerization allows the colloidal assembly to act as a template in which the grafted
PEDOT pattern preserves shape of the PS colloidal template.
dissolution of the PS by ultrasonication in THF.
This is evident upon
Due to PEDOT grafting and the
solubility contrast between PS and PEDOT in THF, the internal PS template is dissolved
127
away after brief ultrasonication (<30 sec) while a PEDOT shroud remains (Fig 4-la). It is
suspected that the retention of the complete hollowed-out, 3-D, HCP geometry is due to
the unique ability of the oCVD process to graft PEDOT to the exterior polymer chains of
the PS beads. This results in enhanced mechanical stability, especially at the tangency
points between adjacent beads, which helps to preserve the top shroud. More rigorous
ultrasonication (>2 min) causes this shroud to break away, revealing the hemispherical
HCP geometry below (Fig 4-lb and 4-1c). These patterns can typically form over areas
as large as 0.3 cm 2 for a 1 ptm diameter template. The typical feature heights and
separation widths of the nanobowls range from 300 to 500 nm and 50 to 150 nm,
respectively, and will vary depending on the template diameter used. Using FeCl 3 as the
oxidant for the oCVD polymerization yields a well-defined PEDOT/PS nanostructure
with a very smooth texture.
Alternatively, it has been shown that CuCl 2 can be used to
produce PEDOT conducting polymer films with tunable nanoporosity.35 This was
coupled with the templating technique described here to produce unique hierarchical
nanostructures (Fig 4-id); internal basalt-like nanoporosity is achieved while maintaining
the large-scale HCP pattern. The high conductivity of oCVD PEDOT films was
maintained in these patterned structures. The bulk resistance laterally across the patterned
PEDOT nanostructures ranged from 3-15 kQ, measured by two-point probe with 3 mm
probe spacing. Due to the wide variation in film thickness inherent in the patterned
structures, the bulk conductivity of the conducting polymer patterns was not calculated;
however, the resistance of the unpatterned PEDOT from the same depositions ranged
from 1-10 kQ which corresponded to conductivities of 2-100 S/cm.
128
..
......
....
..- - - .......
.......
.....
Figure 4-1: SEM images show a PEDOT shroud in which the internal PS template has
been dissolved away by brief ultrasonication in TIHF (a). Rigorous ultrasonication reveals
the hemispherical HCP geometry of the patterned PEDOT nanostructure below (b). Using
FeCl as the oxidant yields a well-defined PEDOT/PS nanostructure with a very smooth
3
texture (c). When CuCl
is used as the oxidant, hierarchically patterned PEDOT
2
conducting polymer films are formed with tunable nanoporosity (d). The inset captures
the morphology of the porous PEDOT on an unpatterned substrate.
The FTIR spectra of the bulk oCVD PEDOT (Fig 4-2a), analyzed in detail
elsewhere, 26 and the self-assembled PS colloidal template (Fig 4-2b) are compared to that
of the oCVD-patterned conducting polymer nanostructures (Fig 4-2c) in which the PS
template was removed by rigorous rinsing and ultrasonication in THF (Fig 4-lb). The
129
........
.....
.........
.
.........................
....
...
..
..
..................
.........
......
.............
...
..
....
................
characteristic peaks of the PS colloidal template (blue) are retained in addition to those of
the bulk oCVD PEDOT (yellow), indicating chemical adhesion of a PS shell to the
surface of the bulk conducting polymer. This retention of the chemical characteristics of
the PS colloidal template is unique to the oCVD process and is not observed when other
CVD polymerization mechanisms are used.
3200
3100
3000
2900
1250
1450
1650
1
Wavenumber (cm )
1050
850
650
Figure 4-2: FT-IR spectra of a blanket oCVD PEDOT conducting polymer film (a), a 2-D
monolayer of 1
sm
diameter polystyrene colloidal template (b), and oCVD-patterned
conducting polymer nanostructures (c) in which the PS template was removed by rigorous
rinsing and ultrasonication in THF. The observation of PS peaks in (c) is evidence of
grafting between the PEDOT nanobowls and the surface of the PS beads.
The grafted PS capping shell on the PEDOT colloidal pattern can be further
utilized for applications by imparting specific functionality via appropriate chemical
modification of the colloidal template. To demonstrate this, we employed commercially
130
available amino-functional PS beads for the PEDOT colloidal patterning process. Upon
patterning PEDOT with these beads, the surface of the PS capping shell contains primary
amine groups. These surface amine moieties can be coupled to a variety of ligands such
as proteins, carbon nanotubes, or nanoparticles (Fig. 4-3a). Since the bulk PEDOT underlayers demonstrate high electrical conductivity and are wired to the functional PS capping
shell via conjugated molecular linkages, these high surface area PEDOT patterns are
attractive for various applications, including biosensors,
electrical drug release,36 and
plasmonic devices.3 7
131
....................
"I'll
- , -",, , ................................................
(a)
Grafted aminofunctional PS
surface layer-]
Grafted
PEDOT
Bulk
=
Amino Functional PS Beads
Grafted Bulk
PEDOT
I
Figure 4-3. Surface amine moieties provide a linkage point between the bulk conducting
polymer nanostructure and various ligands, demonstrated here by attachment of NHS-
tethered fluorescein (a). SEM image of oCVD PEDOT patterned using 1 pm amino-
functional PS beads (b); the inset captures the nanobowl shape, which becomes evident at
the interface with the unpatterned bulk PEDOT.
Fluorescence microscopy shows
fluorescence areas patterned using amino-functional PS beads (c); the inset shows the
interface between the fluorescent patterned regions and the unpatterned bulk PEDOT,
which does not exhibit fluorescence after the identical functionalization treatment (red
arrow).
Figure 4-3b shows SEM images of the oCVD PEDOT patterned using aminofunctional PS beads as the colloidal template. After the non-grafted portion of the amino-
132
functional colloidal template was removed by rigorous rinsing and ultrasonication in
THF, the presence of amino-functional groups on the surface of the patterned PEDOT
nanostructures was easily confirmed by applying an NHS-tethered fluorescent dye (NHSFluorescein, 494 nm excitation wavelength, 521 nm emission wavelength). The
fluorescence from the immobilized dye was captured using a fluorescence microscope, as
shown in Fig. 4-3c. The green fluorescence image mirrors the oCVD PEDOT pattern
shown in Fig. 4-3b. No fluorescence was detected on the unpatterned bulk PEDOT (inset
Fig. 4-3c), and the pattern fluorescence was only observed after functionalization with the
fluorescent dye. This confirms that the PS capping shell on the oCVD PEDOT pattern
contains functionalizable surface amine groups. The ability to tailor the surface
functionality enables the coupling of bioactive molecules or sensing elements to the bulk
PEDOT patterns for various applications.
4.5. Conclusions
We simultaneously patterned and functionalized grafted PEDOT conducting
polymer nanostructures using a simple process combining oxidative chemical vapor
deposition and colloidal lithography. The robust polymer/template interface is established
by covalent coupling of oCVD PEDOT to the aromatic surface groups of the PS
template. Functionalized PS beads can be used to impart specific functional groups to the
surface of the patterned PEDOT layers while maintaining the high conductivity of the
bulk conducting polymer. Here, we used amino-functional PS beads to tether amine
functionality to the conducting polymer nanostructures as demonstrated by the
immobilization of fluorescent ligands. The ability to tether biomolecules or sensing
elements to well-defined arrays of biocompatible conducting polymer nanostructures
makes this technique of great interest for biosensor and cell growth applications;
133
furthermore, the excellent substrate adhesion makes it practical for device applications.
Nanoscale substructure can be introduced into these patterns by replacing the FeCl 3
oxidizing agent with CuCl 2. Parameters such as substrate temperature, bead size, and
bead type allow for precise control over conductivity, pattern dimensions, and imparted
functionality, respectively.
4.6. Acknowledgements
This research was supported in part by the US Army through the Institute for
Soldier Nanotechnologies, under Contract DAAD-19-02-0002
with the US Army
Research Office. This work made use of the shared electron microscopy facility in the
MIT Center for Materials Science and Engineering (CMSE).
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135
Chapter 5
Multi-functional template directed selfassembly towards high density optical data
storage
Nathan J.Trujillo and Karen K. Gleason
136
5.1. Abstract
A strategy for high capacity optical data storage involves surface immobilization
of patterns of multiple photosensitizers
and reading/writing
data by selective
photobleaching using laser excitation. This work uses template directed assembly of
fluorescent colloidal particles within dyed PEDOT-co-TAA copolymer nanobowls to
create bifunctional patterns. Patterns of red fluorescent 200 nm beads were successfully
visualized within blue dyed 1 pm diameter PEDOT-co-TAA copolymer nanobowls. A
process for creating trifunctional patterns is proposed. Additionally, it is anticipated that
pattern uniformity could be optimized by implementing a simple fluidic cell to control
the drying front during the template directed assembly process. Furthermore, this would
reduce the effects of particle/template interaction and provide a strategy for obtaining
trifunctional patterns from binary sets of colloidal crystals.
137
5.2. Introduction
The demand for increasing the capacity of information storage is driven by
advancements in high-definition displays. Future storage demands will soon exceed the
capabilities from advanced optical storage platforms, such as digital versatile disks
(DVDs) and blue ray DVDs. Thus novel techniques are desired for the future of high
density optical data storage.' Ultra-dense, macroscopic arrays of nano-scale elements are
2
purported to revolutionize the microelectronic and data storage industries. Ordered
arrays of cylindrical domains 3 nm in diameter (containing areal densities greater than 10
2
terabits/inch 2) have been created using self-assembled block copolymers. Although this
technique is amenable to magnetic data storage, it would be difficult to implement in
optical data storage because of optical diffraction limits and cross-talk between
neighboring marks.3 Storage densities as high as 75 Gbit/inch 2 have been achieved using
hexagonal closed-packed 50 nm molecular dot arrays of organic photochromes with
'1'/'0' bitwise fluorescence detection. 3 Furthermore, two-color spectral encoding was
demonstrated with gold nanorods doped in a silica sol-gel matrix.I Femtosecond laser
pulses were used to reduce the longitudinal shape of the rods, inducing a blue shift in the
spectral signals. Up to 5000 of these nanorods can be imbedded within a 1 pm 3 focal
volume.
The use of multiple photosensitizers demonstrates notable advantages. The
number of binary recording modes in optical data storage scales as 2", where n represents
the number of individually addressable photosensitizers.4 Therefore, a system containing
two, three, or four different color dyes would represent four, eight, and sixteen-fold
increase in data storage over a homogenous structure, respectively.
138
Polymers are attractive materials for optical applications, as their ease of
fabrication
and
functionalization,
low-cost,
and
high
performance
has
been
demonstrated. 4 Two-photon absorption has been shown to excite resonance energy
transfer from quantum dots to azo-dyes dispersed in a photochromic polymer matrix.
This results in isomerization of the azo-dyes, leading to a dramatic refractive index
change, which allows for optical data storage.5 Periodic fluorescent polymeric
nanocomposites have been successfully used for high density 3-D optical data storage.
Photonic crystals were assembled using fluorescent dye-labeled core-shell latex
nanospheres.
Two-photon laser scanning microscopy was used to photobleach the
optically sensitive fluorescent cores, allowing for bits of information to be written into
the material. Similarly, multi-dye polymer nanocomposites were used for 3-D optical
data recording. 4 Confocal microscopy was used to selectively photobleach different
patterns onto the same spot containing a composite of dyed materials; readout of the
resulting patterns was accomplished by reducing the fluence of the writing laser. Typical
recording densities were ~ 15 Gbit/inch 2 . These techniques require complex synthesis
routs for producing core-shell
dyed polymers,
which makes
the widespread
implementation of these techniques difficult to achieve. For these techniques, typical
laser beam widths range from 350 nm up to several microns.
Using the fabrication techniques discussed in chapter four, we created bifunctional patterns for optical data storage applications. This was accomplished by
assembling commercially
available fluorescently dyed polystyrene beads within
functionalized nanobowls produced from reactive oCVD copolymers of PEDOT and
thiophene-3-acetic acid (TAA). The reactive -COOH groups in the copolymer patterns
were used to covalently immobilize a different color dye onto the patterned oCVD film.
139
Under fluorescence excitation, these patterned structures emit two colors of light: 1)
corresponding to the dyed polystyrene beads and 2) corresponding to an immobilized dye
attached to the functionalized nanobowls. Furthermore, a method for producing trifunctional structures is proposed in this chapter.
5.3. Experimental
Copolymer Pattern Fabrication: Hexagonal-close-packed
copolymer patterns of
PEDOT-co-TAA were produced using the colloidal patterning scheme described in
chapter four. oCVD deposition conditions were adapted from previously published
procedures, 7 and needle valves were used to control the partial pressure of the gas feed at
10 mTorr and 60 mTorr for EDOT and TAA monomers, respectively.
Covalent Immobilization of Reactive Dyes: Blue and green dyes were covalently
immobilized onto PEDOT-co-TAA copolymer patterns using NHS/DCC chemistry.
Green patterns were created by soaking the grafted copolymer patterns in 30 mL of a
1:1:1 (vol) mixture of 0.01 M dicyclohexylcarbodiimide (Alpha Aesar), 0.1 M Nhydroxysuccinimide (99%, Aldrich), and 0.1 M fluorescein-5-thiosemicarbazide (494 nm
excitation wavelength, 521 nm emission wavelength, Molecular Probes) in methanol, for
8 hours at 23'C. The samples were then removed from the mixture and were triple
washed by shaking with 30 mL of methanol in a sealed glass jar. Alternatively, blue
patterns were created by first soaking the grafted copolymer patterns in 30 mL of a 1:1:1
(vol) mixture of 0.01 M dicyclohexylcarbodiimide
(Alpha Aesar), 0.1
M N-
hydroxysuccinimide (99%, Aldrich), and 1 M p-phenylenediamine (99%, Aldrich) in
methanol, for 12 hours at 23'C. The samples were then transferred to a glass jar
containing 30 mL of a 0.04 M solution of AMCA-NHS dye (335 nm excitation, 440 nm
140
emission wavelength, Pierce Scientific) in methanol, for 8 hours at 23'C. The samples
were then removed from the mixture and were triple washed by shaking with 30 mL of
methanol in a sealed glass jar.
Dilute
Template Directed Assembly of Fluorescently Dyed Polystyrene Beads:
solutions of fluorescent and non-fluorescent monodisperse polystyrene beads were used
to assemble the beads within the dyed nanobowl structures. A 1.0 % wt. solution of beads
(1 pm/ violet, 500 nm/ orange, 200 nm/ red nominal diameters, Phosphorex) in water,
was mixed 1:3 with a surfactant solution (Triton X- 100:methanol/1:400 volume) (Fischer
Scientific), cast onto the dyed patterns in a discrete 2.0 p.L droplets, and allowed to dry
under ambient conditions for 15 minutes. The nanobowl template directed the particles to
assemble within the bowl structures, creating a bifunctional pattern. Trifunctional
surfaces were produced from a 1:1 mixture of 1 pm violet beads in surfactant solution
and 200 nm red beads in surfactant solution.
Pattern Visualization and Characterization: The patterned samples were sputter coated
with 5 nm of gold, and SEM images were obtained using a JEOL JSM 6060 with 3 kV
acceleration
voltage. Fluorescence
microscope
images were
obtained
at
100x
magnification using a Zeiss Axiovert 200 inverted microscope with either a FITC or
DAPI filter set. Image analysis was performed using GIMP 2.6 software.
5.4. Results and Discussion
The generic process scheme for producing bifunctional patterns is shown in
Scheme 5-1. Patterned PEDOT-co-TAA copolymers containing free carboxylic acid
groups (Scheme 5-la) are directly reacted with an amine containing dye (FITC-NH 2) to
141
.
........
. .....
....
..........
.
...
. .........
.
.........
.......
...
. ................
....
............
create green patterns (Scheme 5-ib). Alternatively, blue patterns are created by pretreating the patterns with phenylenediamine (PDA) and subsequently reacting with an
AMCA-NHS dye (Scheme 5-1c and 5-1d). Fluorescent beads are then assembled within
the bowls through template directed assembly within the pre-patterned film (Scheme 5le).'
(b) r
(a)
MeOH/NH2-FITC, NHIS, DCC
I
H
8 hours
OOH
OOH
OH
OH
OOH
or
PEDOT-TAA,
PS Shell
Silicon ---
(C)
Substrate
MeOH/PDA, NHS, DCC
NH
2
L.
NH
2
k
NH2
N
NH2
12 hours
NH NH
NH
(e)
(d)
NH
Assemble
fluorescent beads
I q:.J=.
NHS
inMeOH, 8 hours
H
Scheme 5-1: Carboxylic acid groups on patterned oCVD films (a) are directly reacted
with amine containing FITC dye (b) to create green patterns. Indirect reaction with PDA
and AMCA-NHS will create blue patterns (c and d). The dyed nanobowls are then used
for template directed assembly of fluorescent beads (e), which creates bifunctional
patterns.
This process
provides
two
distinct avenues
for selectively coupling
desired
functionalities. Although the above scheme demonstrates the immobilization of dyes, the
surface functionality could be used to immobilize primary amine or NHS containing
142
...................
............
::::::..::
-
-
- -- - --
--
-=
- I -
-
-
-
proteins, antibodies or nanoparticles 7 for sensor applications. Furthermore, as the
particles assembled within the patterns can contain unique surface functionalities, such a
multifunctional surface can be used to monitor the interaction among absorbed
components from a complex biological mixture.9
Figure 5-1 shows an array of 200 nm non-fluorescent polystyrene beads
assembled within PEDOT homopolymer nanobowl patterns.
Figure 5-1:
PEDOT homopolymer
nanobowls
containing statistically distributed
quantities of 200 nm diameter non-fluorescent polystyrene beads (p = 4.95 beads per
bowl, a = 2.13 beads per bowl).
Because the diameter of the beads is significantly smaller than the diameter of the bowls,
up to five adjacent beads can be accommodated across the largest lateral dimension.
However since the diameter of the "bowl" varies in the z-direction, the quantity of beads
143
-
-
-
, __
per bowl is statistically distributed' 0 (Mean = 4.95 beads per bowl, Standard Deviation =
2.13 beads per bowl). By decreasing the diameter difference between the nanobowls and
the beads, the quantity of beads per bowl and the statistical spread will decrease.
Figure 5-2a and 5-2b shows an array of 500 nm fluorescent polystyerene particles
assembled within PEDOT-co-TAA (functionalized with FITC-NH 2 dye) copolymer
patterns. Although the distribution of beads per bowl has decreased, the interaction
between the beads and the template appears to increase. The white arrows in figures 5-2a
and 5-2b indicate assembly defects where there is strong interaction between the beads
and the template. In chapter four we indicated that the walls of the nanobowls contain a
layer of polystyrene. The terrace between the nanobowls does not contain the polystyrene
layer, and appears to strongly interact with the beads, causing the beads to attach to the
top of the terrace. In figure 5-2a, this defect allows two 500 nm beads to assemble within
a single bowl; in figure 5-2b, this defect causes a single bead to assemble outside of the
confining geometry of the nanobowl. This effect is much less pronounced when 200 nm
diameter fluorescent beads are used, as electrostatic interaction energy has been shown to
decrease linearly with particle diameter.10
Figure 5-2c and 5-2d show 200 nm beads assembled within dyed PEDOT-coTAA copolymer patterns. The beads assemble within the nanobowls in an analogous
manner to the 200 nm non-fluorescent beads. Furthermore, the distribution of beads
within the bowls is different than what was observed in figure 5-1. This reflects how the
assembly process can vary depending on the template and bead functionality.
144
Figure 5-2: 500 nm diamter fluorescent orange polystyerene particles assembled within
dye) copolymer patterns demonstrate
PEDOT-co-TAA (functionalized with FITC-NH
2
two types of defects: two particles assembling within one bowl (a) and particles attaching
to the terrace of the nanobowl structure (b). 200 nm red beads assembled within AMCA-
NHS dyed PEDOT-co-TAA copolymer patterns (c) (d) assemble in an analogous manner
to the 200 nm diameter non-fluorescent beads.
Although it is difficult to quantify the effects of surface interaction on the quality
of the template directed assembly, it is essential to analyze the factors that may influence
the uniformity. Various studies have determined that there are three major forces that act
upon the colloidal particles throughout the self-assembly process: gravitational forces,
145
electrostatic forces, and capillary forces.'
-14
As the density of the beads is approximately
equal to that of the wetting media, gravitational forces are usually negligible."
Electrostatic forces become particularly important when there is an attractive force
between the beads and the template. This factor is responsible for the beads randomly
sticking to the template in Figure 5-2b. Previously reported strategies for overcoming this
limitation have been to modify the surface wettability in order to create a repulsive
interaction with the particles
13,15
or to directly change the surface charge of the template
by controlling the pH value of the dispersion medium. 10 "'
Capillary forces from the dewetting liquid front provide the most important
driving force to push the colloidal particles into the template holes. By properly
engineering a fluidic cell for controlling the dewetting process, the effect of surface
interaction can be eliminated. Although the procedure that was employed in chapter three
can create uniform monolayers of hexagonal-close-packed particles on a planar substrate,
this procedure has notable short comings for the template directed assembly reported in
this chapter. In order to ensure uniform template assisted assembly over large areas, a
simple fluidic
cell
should be constructed
according
to previously published
procedures. 11,16 This would create a uniform drying front and allow a greater degree of
control over the magnitude of the capillary force exerted onto the colloidal particles.
To demonstrate the potential of using a template directed assembly process for
optical data storage, the patterns depicted in figure 5-2c and 5-2d were visualized under a
fluorescence microscope. Figure 5-3a shows an optical micrograph of the 200 nm red
beads
assembled within AMCA-NHS
functionalized
PEDOT-co-TAA
nanobowl
patterns. Only the 1 pm diameter nanobowls are visible under the white light
illumination. When the patterns are illuminated using a DAPI filter set, the two dyes
146
become visible (Figure 5-3b). Image analysis was performed to decouple the respective
dye signals. The blue regions correspond to the PEDOT-co-TAA regions that were
functionalized with the AMCA dye (figure 5-3c). This represents the regions along the
perimeter of the bowls. The yellow regions correspond to the 200 nm beads that are
assembled within the nanobowls (figure 5-3d). Although the actual bead color is red, the
DAPI emission filter only allows for the yellow component of light to pass. The
hexagonal pattern of the yellow emission indicates that the 200 nm particles are
assembled within the bowls. This image demonstrates a proof of concept that bifunctional
patterns can quickly be achieved through template directed assembly. Through proper
laser excitation, each color could be selectively photobleached to record different
information on the same spot. This process has previously been demonstrated as a
feasible method for reading/writing data without cross-talk.4 Furthermore, an important
consideration when using multiple dyes for data recording is the tradeoff between
recording time and photostability of the dyes used. In order to reduce the destructive
readout of the patterns, high photostability is preferred. Therefore, when evaluating these
patterns for optical data storage, it might be necessary to vary the dye components to
optimize the photostability and recording time.
Figure 5-3e shows a fluorescence micrograph for the template directed assembly
of 1 prm diameter dyed beads onto FITC-NH 2 functionalized PEDOT-co-TAA
nanobowls. Since the center to center distance between the nanobowls is identical to the
diameter of the beads, the beads in the top layer are hexagonally-close-packed and are in
physical contact with one and other. These packed beads obscure the underlying
template, which limits the applicability towards optical data storage. Thus, future studies
147
I...........
.......
........
......
....
..................
.
should focus on using either 700 nm, 500 nm, or 200 nm dyed polystyrene beads so that
the dyed regions along the perimeter of the bowls remain exposed.
Figure 5-3:
Optical micrograph of 200 nm red beads assembled within AMCA-NHS
functionalized PEDOT-co-TAA nanobowls (a). When these patterns are illuminated using
a DAPI filter set, the two dyes become visible, demonstrating bifunctional patterns (b).
Image analysis decouples the dye signal corresponding to the bowl perimeter(c) from the
fluorescent bead signal (d). Fluorescence micrograph for the template directed assembly
of 1 pm diameter dyed beads onto FITC-NH functionalized PEDOT-co-TAA nanobowls
2
148
(e). Trifunctional patterns using two distinct fluorescent beads assembled atop FITC-NH
2
dyed nanobowls resulted in an irregular assembly (f).
Figure 5-3f demonstrates an attempt to produce trifunctional patterns using two
distinct fluorescent beads assembled atop FITC-NH 2 dyed nanobowls (1 Pm diameter
blue beads and 200 nm red beads were used). The lack of control over the drying process
resulted in irregular assembly of both sets of particles, confirming the limitations of the
experimental procedure in creating a controlled assembly. By precisely controlling the
drying process, Blaaderen and coworkers were able to create binary colloidal crystals
consisting of silica beads of two different diameters.
7
By controlling the drying front,
three distinct binary structures can be created. Similarly, asymmetric dimers of different
size red and green beads were assembled within pre-patterned templates. This was
achieved merely by sequentially flowing dispersions of different colloids through the
same fluidic cell." Moreover, the step-by-step deposition of 2-D arrays successfully
created Kagome structures from red and green beads assembled over prepatterned
templates.16 Thus, by implementing a controlled fluidic cell in our template directed
assembly experiments, we can practically achieve trifunctional patterns using two distinct
fluorescent beads. The presence of three distinct photosensitizers would increase the
amount of binary recording modes and enhance the applicability for high density optical
data storage.
5.5. Conclusions
A simple process for creating bifunctional dyes patterns is presented as a first step
towards surfaces for optical data storage applications. Nanobowl templates produced
from PEDOT-co-TAA copolymers were used to covalently immobilize green or blue dye
149
molecules through NHS/DCC chemistry. The dyed nanobowls were used as templates for
directing the assembly of 200 nm, 500 nm, or 1 pm fluorescent polystyrene beads. When
the bead diameter was significantly smaller than the diameter of the nanobowls, the
amount of beads per bowl was statistically distributed. High interaction between 500 nm
beads and the terrace between the nanobowls resulted in beads assembling outside of the
confined regions. Furthermore, use of 1 pm beads obscures the underlying dyed template.
Using fluorescence microscopy, patterned dyes from the nanobowl template and the 200
nm particles were successfully visualized, indicating that bifunctional patterns can
quickly be achieved through template directed assembly. In order to ensure uniform
template assisted assembly over large areas, a simple fluidic cell should be constructed.
This would reduce the statistical variation of particles within the nanobowl template,
reduce the effect of particle/template interaction, and provide a practical route for
creating trifunctional patterns using two distinct fluorescent beads. Through proper laser
excitation, these bifunctional and patterns could be photobleached for the reading and
writing of optical data.
5.6. References
1
J. W. M. Chon, C. Bullen, P. Zijlstra, and M. Gu, Advanced Functional Materials
17, 875-880 (2007).
2
S. Park, D. H. Lee, J. Xu, B. Kim, S. W. Hong, U. Jeong, T. Xu, and T. P.
Russell, Science 323, 1030-1033 (2009).
3
H. Port, S. Rath, M. Heilig, and P. Gartner, Journal of Microscopy-Oxford 229,
463-468 (2008).
4
I. Gourevich, H. Pham, J. E. N. Jonkman, and E. Kumacheva, Chemistry of
Materials 16, 1472-1479 (2004).
5
X. P. Li, J. W. M. Chon, R. A. Evans, and M. Gu, Applied Physics Letters 92
(2008).
6
B. J. Siwick, 0. Kalinina, E. Kumacheva, R. J. D. Miller, and J. Noolandi, Journal
of Applied Physics 90, 5328-5334 (2001).
7
S. Vaddiraju, K. Seneca, and K. K. Gleason, Advanced Functional Materials 18,
1929-1938 (2008).
150
8
9
10
12
13
14
15
16
17
M. E. Abdelsalam, P. N. Bartlett, J. J. Baumberg, and S. Coyle, Advanced
Materials 16, 90-+ (2004).
S. G. Im, K. W. Bong, B.-S. Kim, S. H. Baxamusa, P. T. Hammond, P. S. Doyle,
and K. K. Gleason, Journal of the American Chemical Society 130, 14424-14425
(2008).
Y. H. Kim, J. Park, P. J. Yoo, and P. T. Hammond, Advanced Materials 19, 44264430 (2007).
Y. Yin, Y. Lu, B. Gates, and Y. Xia, Journal of the American Chemical Society
123, 8718-8729 (2001).
M. Rycenga, P. H. C. Camargo, and Y. N. Xia, Soft Matter 5, 1129-1136 (2009).
M. J. Lee, J. Kim, and Y. S. Kim, Nanotechnology 19 (2008).
T. Kraus, L. Malaquin, E. Delamarche, H. Schmid, N. D. Spencer, and H. Wolf,
Advanced Materials 17, 2438-+ (2005).
P. Maury, M. Escalante, D. N. Reinhoudt, and J. Huskens, Advanced Materials
17, 2718-+ (2005).
T. Onodera, Y. Takaya, T. Mitsui, Y. Wakayama, and H. Oikawa, Japanese
Journal of Applied Physics 47, 1404-1407 (2008).
K. P. Velikov, C. G. Christova, R. P. A. Dullens, and A. van Blaaderen, Science
296, 106-109 (2002).
151
Chapter 6
UV and e-beam patterning of vinyl coupling
agents: towards resist-free photolithography
of polymeric thin films
Nathan J.Trujillo and Karen K. Gleason
152
6.1. Abstract
Deep UV lithography was used to pattern vinyl monolayers that were covalently
tethered to silicon substrates. The unexposed monolayer covalently links iCVD or oCVD
polymers deposited onto the pre-patterned substrates. The unexposed regions of the
substrate contain grafted polymer patterns that were revealed by removing non-tethered
polymer with an environmentally friendly solvent, IPA. This technique successfully
patterned p(CHMA-co-EGDA) and p(butyl acrylate) without the use of a photoresist.
Wetting contrast was observed on 50 pm linewidths of grafted thin layers (<30 nm) of
oCVD PEDOT. Furthermore, e-beam lithography successfully patterned 1 Pm linewidths
of grafted monolayers using power doses less than those required for traditional
photolithography. Although these processes must be optimized before they can become
commercially viable, this work represents an incremental step towards materials
reduction and process simplification in lithography.
153
6.2. Introduction
There are two approaches for covalently tethering polymers to surfaces. The
"grafting to" approach requires the reaction between preformed end-functionalized
polymer chains with a suitable substrate that will bind covalently with the polymer.
"Grafting from" is accomplished by treating a substrate with a substance from which
polymerization is initiated. The latter approach is more attractive for producing high
density polymer brushes' where the theoretical maximum density for polymers deposited
2 2
on fully hydroxylated silica is 4.6 groups/nm . Historically, these grafting techniques
have been performed in the liquid phase and generally result in limited film thickness.3 4
Andao and coworkers patterned polymer brushes by selective activation of tethered
photoinitiators with UV light, followed by subsequent polymerization. However, the
polymerization was very slow and the films were only about 25 nm thick.5 Alternatively,
patterns were created by using an e-beam to bombard and decompose tethered initiators.
Although lateral pattern resolution was 150 nm, it took over 12 hours to deposit 50 nm of
polymer.6 Photoinitiated CVD (piCVD) was used to grow CHMA films from initiator
species patterned by micro contact printing.7 This technique improved throughput for
additive polymer patterning tremendously, however, the inability to continuously supply
initiating species from the vapor phase limits the ultimate film thickness obtainable.
In an iCVD deposition, initiator is continually supplied, thus allowing for the
deposition of thick polymer brushes when copolymerized with a crosslinker. We propose
a method for creating thick films of patterned polymer by using deep UV light or e-beam
lithography for decomposing the vinyl anchoring sites that can be used for free radical
grafting polymerization.
2
DeSain and coworkers recently studied the photolysis
mechanisms for trichlorovinyl silane and allyltrichlorovinylsilane, common vinyl silane
154
coupling agents, and determined that the formation of volatile vinyl radicals was
dominant at 193 nm. 8 They also found that both the adsorption cross section and quantum
efficiency were orders of magnitude larger at 193 nm than at 256 nm.8 In principle,
commercially available 193 nm steppers can be used for irradiation and traditional
lithography masks can define exposure patterns. Because only a monolayer needs to be
irradiated, this technique shall theoretically require much less energy density when
compared to traditional photoresist irradiation (0.8 mJ/cm 2 versus > 15 mJ/cm 2). 9
This concept of monolayer irradiation has been pioneered by Sugimura and
coworkers. 10-1 They used excimer lamp excitation at 193 nm and 172 nm to photolyze
organosilane monolayers that were grafted onto hydrolyzed silicon substrates. They
determined that there are indeed two competing mechanisms for the photolysis
mechanism. In the presence of atmospheric oxygen, the deep UV light can create reactive
ozone molecules,' 0 which react with the tethered monolayer through photoxidation. This
phenomenon competes with the direct photoloysis of the silane layer. Furthermore, the
unrestricted diffusion of the reactive ozone can cause feature widening, thus, high
resolution features can be created by reducing the overall system pressure. Using this
method they have demonstrated patterns with feature sizes as small as 565 nm.
The objective of this work is to demonstrate a proof of concept for the resist-free
patterning of iCVD and oCVD polymers. By using deep UV light for irradiating
covalently coupled vinyl silane monolayers through shadow masks (Figure 6-la and 6lb), iCVD polymers will selectively adhere to the unexposed sites (Figure 6-1c); the
patterned polymer features can be resolved by rinsing the blanket films in a solvent
(Figure 6-1d). The patterned features from the monolayer are then transferred to grafted
polymer films. The adhesion contrast between the grafted portions of the blanket film and
155
...................
.
.............
....
..........
..
.........
the ungrafted regions result in the removal of the ungrafted portions by solvent rinsing.
Eliminating the use of photoresists avoids dectructive plasma etching14 and can reduce
the overall environmental impact from semiconductor manufacturing.1 5
(b)
(a)
Quartz Shadow
Mask and Deep UV
Light Exposure
Vinyl Silane Treated Wafer
Deposit Blanket
Polymer Film Via iCVD
~monolayer
(c)
(d)
Rinse/Sonicate With
EHS Friendly
Solvent
Figure 6-1: Generic processing scheme for resist-free lithography. A vinyl silane treated
wafer (a) is exposed to deep UV light through a shadow mask (b). An iCVD polymer
blanket layer is deposited onto the irradiated substrate (c). The polymer film covalently
adheres to the unexposed regions of the substrate. Rinsing in a solvent removes the
untethered polymer layers and reveals patterned iCVD polymer (d).
6.3. Experimental
Resist-free polymer patterning was performed using the general procedure in
Figure 6-1. After a 15 minute oxygen plasma treatment, clean silicon wafers
(Waferworld) were dipped in de-ionized water (Aldrich) and baked for 30 minutes in a
nitrogen purged vacuum oven at 100"C.
156
Vinyl silane monolayers were grafted by evaporating 1 mL of monofunctional
trichlorovinylsilane (TCVS 98%, Aldrich) in a heated vacuum oven and allowing the
vapor to sit stagnant in vacuum for 1 hr. The chamber was then purged with nitrogen
under vacuum and allowed to outgas for an additional 30 min to remove any unreacted
species from the wafers. Water contact angles on the treated silicon ranged from 75"-780,
thus confirming that the monolayer grafting was successful.
A quartz shadow mask (Photronics) containing patterns of squares between 200
pim -300 pim or line patterns ranging from 1 pim - 50 ptm was placed over the silane
treated wafer. A mercury (Hg) lamp (300 W) was placed inside an arc lamp housing
(Thermo-Oriel), with a beam turner and full reflector directing the UV light onto the
substrate, through the reticle, approximately 2.5 cm away from the reflector. The mercury
emission spectrum has a small intensity tail at 193 nm, which is believed to photolyze the
vinyl bonds. Typical treatments times range between 12-20 hours. Using previously
published techniques,16 iCVD was used to deposit 200 nm thick blanket copolymer films
of cyclohexyl methacrylate (CHMA, Aldrich) and ethylene glycol diacrylate (EGDA,
Aldrich) (4 minute deposition) and homopolymer films from butyl acrylate
onto an
unpatterned silane treated wafer, a patterned silane treated substrate, and bare silicon.
Both sets of three samples were then rinsed in isopropanol (IPA 99%, Aldrich) for 5
seconds.
Additionally, using the deposition conditions reported in chapter four, oCVD was
used to deposit a 30 nm PEDOT coating onto pre-patterned substrates. This film was
ultrasonicated in IPA for 20 minutes. Water vapor was condensed onto the PEDOT
patterns from an Erlenmeyer flask with 100 mL of water heated to 600. The flask was
outfit with a stopper containing plastic tubing, and orienting the open end of the tube over
157
the patterned regions. The compositions for all polymer films were confirmed, albeit not
reported, via FT-IR.
E-beam lithography was performed using a Leica VB-6HR electron beam
lithography system with doses ranging from 800 pC/cm 2- 6000 pC/cm 2.
Contact angle measurements were performed with a contact angle goniometer
with automatic dispenser (Rame'-Hart Model 500) using 2.5 piL water droplets.
FT-IR spectra were obtained using a liquid nitrogen cooled Mercury-CadmiumTelluride (MCT) detector over the range of 700 cm-1- 2000 cm-1 at 4 cm-1 resolution
averaged over 64 scans, and baseline corrected.
Optical micrographs were captured using a Olympus CX-41 microscope with a
Olympus TH4-100 fiber optic backlight. Atomic force microscope images were
generated using a scanning Probe microscope (Digital Instruments, Dimension 3100) in
tapping mode with a 1.0 Hz scan rate.
Film thicknesses were measured using spectroscopic ellipsometry (J.A. Woollam
M-2000S). Data was collected at 68' incidence angle for 190 wavelengths between
315nm and 718 nm. The data was fit to a Cauchy-Urbach model from which the
thickness values were extracted.
6.4. Results and Discussion
To demonstrate the UV photolysis of surface tethered vinyl, a blank vinyl silane
treated wafer was irradiated under the UV lamp without a photomask. Infrared spectrum
and water contact angles were acquired before and after irradiation (Figure 6-2). The asgrafted monolayer, prior to photolysis (Figure 6-2a), shows absorption peaks at 733 cm ,
1009 cm-1, 1271 cm-1, 1407 cm-1, 1604 cm-1, which all correspond to the presence of
vinyl.18 After UV irradiation, these peaks no longer remain (Figure 6-2b), indicating that
158
..
...
. .........
.
.....
...
..............
the silicon surface no longer contains any vinyl. This assertion is further confirmed by
water contact angle which decreases from 970 to 50", and shows the transition from a
hydrophobic to a hydrophilic regime when surface-tethered vinyl groups are removed the
underlying oxide is revealed.
1700
1600
1500
1400
wavenumber
1100
1200
1300
1000
900
(cm- 1)
Figure 6-2: FT-IR spectra for as-grafted TCVS monolayer on a silicon substrate (a) and
after 20 hours of photolysis with a UV lamp (b). The grey arrows indicate the position of
the photolyzed vinyl groups, which are present in the as-grafted film. The reduced water
contact angle reflects the removal of the organic monolayer and the subsequent exposure
of the underlying native oxide from the substrate.
After the iCVD deposition, the bare silicon sample did not contain any polymer
after rinsing, the blank treated wafer retained the entire film, and the patterned wafer
revealed 200 nm thick square patterns of
p(CHMA-co-EGDA) (Figure 6-3a)
159
corresponding to the unexposed regions of the photomask. This represents a marked
success when compared to solution based techniques for patterning polymer brushes,
which require 12 hr to deposit ~ 50 nm
6
and more recent vapor deposition techniques
which required 45 min to deposit 100 nm.7 Butyl acrylate was patterned without a cross
linker and generated patterns less then 20 nm thick, after having deposited about 75 nm
before rinsing with IPA (Figure 6-3b). To produce thicker film patterns, a cross linking
agent, such as EGDA, is required. This increases the average size of the grafted polymer
chains, which is necessary as the liftoff step removes all polymer species but those
covalently bound to the surface.
Figures 6-3c and 3d demonstrate the wetting contrast that is achieved after
patterning grafted thin layers (<30 nm) of PEDOT via oCVD. The darker areas contain
condensed water vapor that has preferentially wets the regions of the substrate exposed to
UV light. The 50 pm linewidths containing PEDOT appear lighter in color and do not
favorably condense the moisture.
160
.
.
..
.....
..........
....
.........
..
...
.......
. ....
.............
.....................
Figure 6-3: 200 nm thick iCVD patterns were created from p(CHMA-co-EGDA) (a),
whereas only 20 un thick patterns from iCVD p(butyl acrylate) remain after liftoff in IPA
(b). The use of a crosslinker can help generate thick patterns after liftoff. Wetting contrast
that is achieved after patterning grafted thin layers (<30 nm) of PEDOT via oCVD (c and
d). The darker regions correspond to water condensation on the UV exposed regions.
PEDOT is located in the lighter regions.
We extended the basic concept of macroscopic polymer pattern definition by
lithography at the monolayer level, to e-beam writing. Several line patterns ranging from
2 ptm to 10 nm were written onto the vinyl silane treated wafers (Figure 6-4a). These
samples were then coated via iCVD and subsequently rinsed in IPA. Approximately 90
161
..................
........
nm of p(CHMA-co-EGDA) was deposited via iCVD. Liftoff was performed with 5 X 5
second rinses of IPA. Figure 6-4b contains an optical microscope image which shows
successful recovery of the e-beam patterns. The polymer should and did remain
everywhere but in the pattern pitch, which is where the e-beam irradiation had taken
place.
0
nm
Decreasing
Line Width
(a)
1pm
( I
1
Figure 6-4: Linewidth patterns ranging from 2 pm to 10 nm were written onto the vinyl
silane treated wafers by e-beam irradiation (a). iCVD was used to deposit a blanket film
of p(CHMA-co-EGDA) copolymers onto the pre-pattened substrates. These films were
subsequently rinsed in IPA. An optical micrograph (b) indicates that polymer features
smaller than 1 pm could not be resolved.
162
...............
.......
........
.............
AFM images (Figure 6-5) indicate that a poor iCVD deposition lead to island
polymer growth instead of a uniform blanket; however, it is clear that 1 pm linewidths
were recovered. An AFM line scan indicates that the average height of the patterned
polymer lines was approximately 33 ±3 nm with an average FWHM of about 1.01 ± 0.01
gm. Here, the pattern pitch between the lines indicates regions where the untethered
polymer had been removed.
Figure 6-5: AFM image of 1 sm p(CHIMA-co-EGDA) linewidths developed from e-beam
pre-patterned substrates. The white line shows the region corresponding to the
accompanying line scan (bottom), which indicates an average height of the patterned lines
of 33 ± 3 nm with an average FWHM of 1.01 + 0.01 pm.
163
..........
...
..........
...
..............
.............
..............
For smaller linewidths (<500 nm) there is extensive line bridging which gives rise
to features which look like the capital letter 'H' (Figure 6-6). This is likely a caused by
large polymeric length scales which span adjacent features. After liftoff it may be
possible to have a single crosslinked polymer unit covalently linked to two distinct
features, "bridging" over the pattern pitch. The likely case is that this lateral length scale
is somewhere between 500 nm and 1 pim, which is larger than the pattern
pitches/linewidths and is responsible for the bridging. Therefore, this process should be
optimized by performing a systematic variation of crosslink density to determine the
length scale threshold where line bridging occurs.
Figure 6-6: AFM images showing smaller polymer linewidths (<500 nm). For smaller
features, there is extensive line bridging which gives rise to features which look like the
capital letter 'H' (indicated by the white circle).
As 193 nm steppers are currently in commission within most semiconductor
foundries, a key to demonstrating success in resist-free photolithography is to adapt a
164
monolayer irradiation process to commercially available equipment. Although this
technique needs to be optimized before it can become commercially viable, this work
represents an incremental step towards materials reduction and process simplification in
lithography.
6.5. Conclusions
UV and e-beam irradiation of grafted vinyl monolayers has been successfully
used for resist-free patterning of iCVD and oCVD polymers. UV irradiation of TCVS
monolayers was used to create iCVD patterns 200 nm and 25 nm thick from p(CHMAco-EGDA) and p(butyl acrylate) polymers, respectively. Wetting contrast was observed
on 50 pm linewidths of grafted thin layers (<30 nm) of oCVD PEDOT. Adhesion
contrast between the grafted and ungrafted portions of the films deposited onto prepatterned substrates allowed for iCVD and oCVD patterns to be developed in an
environmentally friendly solvent, IPA.
Selective e-beam irradiation of grafted
monolayers requires doses less than 800 pC/cm 2 to achieve monolayer patterning.
Patterned polymer lines were obtained for p(CHMA-co-EGDA) polymers, with features
33 ± 3 nm high and FWHM of about 1.01 ± 0.01 pam.
The energy and materials
requirement for this process is substantially lower than what is used in traditional
photolithography patterning, as no photoresist is required. Future work should be directed
at optimizing this process for integration with commercial steppers. Nevertheless, this
work represents
an incremental step towards
materials reduction
and process
simplification in lithography processes.
6.6. Acknowledgements
The authors would like to acknowledge the support from the NSF/SRC
Engineering Research Center for Environmentally Benign Semiconductor Manufacturing.
165
We would like to thank Dr. Marvin Paik at Cornell University for his assistance with ebeam lithography.
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14
P. Berruyer, F. Vinet, H. Feldis, R. Blanc, M. Lerme, Y. Morand, and T. Poiroux;
Vol. 16 (AVS, 1998), p. 1604-1608.
G. Percin and B. T. Khuri-Yakub, Ieee Transactions on Semiconductor
Manufacturing 16, 452-459 (2003).
K. Chan and K. K. Gleason, Macromolecules 39, 3890-3894 (2006).
16
17
K. K. S. Lau and K. K. Gleason, Macromolecules 39, 3688-3694 (2006).
18
S. Y. Shen, G. A. Guirgis, and J. R. Durig, Structural Chemistry 12, 33-43 (2001).
166
Chapter 7
Conclusions and future work
167
7.1. Conclusions
The principle objective of this thesis was to create porous dielectric films by
initiated chemical vapor deposition (iCVD) and to pattern these films using
environmentally benign processes. Mechanically robust dielectric films with k- 2.15
were patterned to feature sizes of 25 nm using environmentally innocuous techniques.
The novel patterning techniques introduced in this thesis are extendible to iCVD and
oCVD polymers and can enable a wide range of applications. The areas of interest to the
scientific community that this thesis primarily addresses are in realm of environmentally
focused deposition of novel dielectric materials and non-conventional nanopatterning of
broad material sets for semiconductor, bioelectronic, and data storage applications.
7.2. Ultra-low Dielectric Constant Films Deposited by iCVD
Films grown from the cyclic monomer tetravinyltetramethylcyclotetrasiloxane
(V4D4) via iCVD become mechanically robust when they are thermally cured in air. The
solventless iCVD method consumes an order of magnitude lower power density than the
traditional Plasma Enhanced Chemical Vapor Deposition, and preserves the ring structure
and organic substituents in the as-deposited films. Silsesquioxane cage structures in the
annealed films appear in the Fourier transform infrared and Raman spectra. The
beneficial formation of intrinsically porous silsequioxane cages result from annealing in
air. Greater hardness and modulus is observed in films with connectivity numbers above
the percolation of rigidity. Removal of labile hydrocarbon moieties results in oxidation of
films while simultaneously inducing porosity. In this process, the typical trade-off
between improved mechanical properties and higher dielectric constants is avoided.
Films annealed at 410 C have a dielectric constant of 2.15, hardness and modulus of 0.78
GPa and 5.4 GPa, respectively.
168
7.3. Grafted Functional Polymeric Nanostructures by Colloidal Lithography
Colloidal lithography, combined with initiated chemical vapor deposition (iCVD),
provide an inexpensive, simple, and environmentally friendly process for creating robust
well-ordered arrays of functional patterned polymeric nanostructures up to 500 nm in
height. These grafted "nanobowl" patterns were produced for a broad material set of
functional organic, fluorinated, and silicon containing polymers and fully retain the
organic functionality of their monomeric precursors These patterns are robustly tethered
to the underlying and withstand aggressive solvent rinsing. We patterned p(V4D4) down
to 25 nm without the need for environmentally harmful solvents. Capillary force
lithography was used to create topographical templates for large-scale orientation of the
nanoparticle assembly. Multi-scale polymeric patterns were created without the direct
need for expensive lithography tools.
7.4. Conducting Polymer Nanostructures for Advanced Bioelectronic Applications
Patterned and amine functionalized biocompatible conducting polymer
nanostructures were fabricated using grafting reactions between oxidative chemical vapor
deposition (oCVD) PEDOT conducting polymers and amine functionalized polystyrene
(PS) colloidal templates. These patterns preserve the advantageous electrical properties of
the bulk conducting polymer. This surface functionality affords the ability to couple
bioactive molecules or sensing elements for various applications. Fluorescent ligands
were immobilized onto the amine-functional PEDOT nanopatterns and nanoscale
substructure was introduced into the patterned oCVD layer by replacing the FeCl 3
oxidizing agent with CuCl 2.
169
7.5. Multi-functional Template Directed Assembly Towards Optical Data Storage
Fluorescent colloidal particles were assembled within dyed PEDOT-co-TAA
copolymer nanobowl templates to create bifunctional patterns. Using fluorescence
microscopy, patterns of red fluorescent 200 nm beads were successfully visualized within
blue dyed 1 pm diameter PEDOT-co-TAA copolymer nanobowls. These bifunctional
patterns can be easily synthesized, and are attractive for optical data storage applications
Pattern uniformity could be optimized by implementing a simple fluidic cell to control
the drying front during the template directed assembly process, and can enable the
fabrication of trifunctional surfaces.
7.6. UV and E-Beam Patterning of Vinyl Coupling Agents for Polymer Patterning
In the final work of this thesis, UV lithography was used to pattern covalently
tethered vinyl monolayers. iCVD or oCVD polymers deposited onto the pre-patterned
substrates graft to the unexposed regions. Non-tethered polymers were removed with an
environmentally friendly solvent, IPA. p(CHMA-co-EGDA) and p(butyl acrylate) were
successfully patterned without the use of a photoresist. Wetting contrast was observed on
grafted thin layers (< 30 nm) of oCVD PEDOT. Grafted monolayers 1 pm in width were
patterned with e-beam using power doses smaller than those required for traditional
photolithography. Although this process shows promise for resist-free photolithography,
further optimization is required to create a commercially viable process.
7.7. Future Work
The studies described in this thesis lay the basis for additional, applicationoriented work. In particular, the approach of this thesis has been to explore novel
techniques in iCVD and oCVD to increase the general applicability of these platform
170
technologies. The novel processes reported are merely a means to an end, and benefit
from optimization and fine tuning.
There are several avenues for improving the p(V4D4) dielectric films. A first
order improvement would be to the thermal stability of the films. The thermal curing
process reported in chapter two results in approximately 45% film loss. An interesting
study would be to examine the film shrinkage for films deposited at elevated substrate
temperatures (ca. 300*C). This form of "soft baking" has been shown to increase the
thermal stability of PECVD low-k films. Furthermore, low thermal stress is required for
successful film integration. Four cured p(V4D4) films were shipped to Junjun Li at TEL
LTD. for thermal stress analysis; however, budgetary reasons did not allow for the
independent characterization of the samples.
There are many target applications for the patterning work reported in chapters
three and four. Although this thesis focused on the fabrication of novel nanostructured
materials, such as functional, fluorinated, and conducting polymers, the challenge
becomes to use these materials in a target application. For example, the robust multi-scale
patterns reported in chapter three can be used for creating optical waveguides or cell
growth scaffolds. Christy Petruczok has recently created high surface area nanobowl
structures from p(vinyl pyridine), for detection of nitro-aromatic explosives. The
functionalized conducting polymer nanobowls reported in chapter three can be used to
construct biosensors or as a platform for cell stimulation.
Two major issues remain unresolved from the multi-functional template assisted
assembly study reported in chapter five. The absence of large-scale pattern uniformity
would preclude the use of this process for high density optical data storage. Large scale
pattern uniformity can be greatly improved through strict control over the drying process.
171
Further study will require a custom built fluidic cell, which can easily be fabricated using
previously published techniques. Moreover, an optics set-up is necessary to evaluate the
ability to read and write multiple bits of data to the same regions of the multi-functional
patterns. Dr. Steve Kooi at the ISN can provide the necessary expertise in arranging the
appropriate lasers, and filters, for selective photobleaching (data recording). Fluorescence
microscopy will remain the tool of choice for data readout.
A practical application for the patterned p(CHMA) reported in chapter six can be
towards the creation of airgap structures for advanced dielectric stacks. This process of
resist-free lithography, however, still requires systematic study of the effects of crosslink
density on the minimum resolvable feature width. Although the technique is quite robust
for feature widths much greater than the thickness of the film, it becomes limiting for
lateral features smaller than 1 pm. Once this study is complete, the ultimate goal is to
evaluate this process on a commercial 195 nm stepper. Demonstrating the commercial
viability of this resist-free process would represent a significant step towards reducing the
overall environmental impact of photolithography processes.
172
Appendix A
Integrative Perspective Capstone*
Adapted from 100K Business Plan Submission
173
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Revolutionary solutions for revolutionary displays
Nathan Trujillo
Eric Lam
Kiran Divvela
Yoo Mi Hong
Hai Liu
Faculty Advisor: Professor Fiona Murray
174
EXECUTIVE SUMMARY
hLED Technologies is a company that offers technology development and licensing
solutions for manufacturing hybrid inorganic-organic Light Emitting Diodes (hLEDs) to
display manufacturers. Our patent pending technology developed in Professor Karen
Gleason's lab at MIT is similar to the emerging Organic Light Emitting Diodes (OLEDs)
technology but offers more robustness, enabling longer lifetimes, a broader range of
applications, and lower manufacturing costs. Because of the difficulties in
manufacturing and slow adoption rate of OLEDs, we have a unique opportunity to
leapfrog OLED technology. Our target customers will be display integrators for military
and avionics products, who highly value the improvements but have not adopted OLED
technology due to low product lifetimes. We will approach Vuzix, Parvus, and other
display integrators about forming co-development partnerships to take our technology
from proof-of-concept to prototype and subsequently expand into the rest of the
display market.
Market Opportunity
The display market can be broadly segmented by display sizes: large screens, midsized
screens, and small screens. Liquid Crystal Displays (LCDs) continue to dominate the small
and midsized display markets. The newest LCDs use LED backlighting to produce white
light, which issubsequently filtered to produce a range of colors. Because the majority
of the produced light iswasted in filtering, LCDs are inherently inefficient. Furthermore,
filtering limits the darkest black that can be produced, and hence reduces the display's
dynamic range or contrast ratio.
To solve these two major problems associated with LCDs, companies have been
developing OLED displays. Instead of filtering light, OLEDs produce light: with no light to
filter, blacks are blacker and light efficiency is improved. Unfortunately, OLEDs are
sensitive to moisture and oxygen, which complicates the manufacturing process and
reduces the material durability. These reliability problems have slowed the transition to
OLED displays. Additionally, OLED materials have inherently low lifetimes. Currently
applications with OLED displays are very few and concentrated in the consumer
electronics market, which only comprises4% of the display market, but is expected to
increase ten-fold in the next six years and isforecasted to reach $7Billion by 2016.
Product Description
Our patent-pending technology has similar device architecture to OLEDs. In OLEDs, an
organic emissive layer issandwiched between two conducting layers. The key difference
between OLED and our hLED technology is our emissive layer is inorganic quantum dots.
Because the layer is inorganic, it is more robust and able to withstand conditions that
ruin their OLED counterparts. While this seems like a simple layer substitution, the
increased robustness enables significant cost reductions because we do not need the
costly additional equipment, processing, and packaging that OLED manufacturing
requires.
175
Competitive Advantage
LED displays are separated into two categories: inorganic and organic. OLEDs have been
hyped as the replacement for inorganic LEDs as they offer improvements in mechanical
flexibility, inexpensive processing, and don't require an LCD to filter light. These
improvements, however, come at the loss of stability, longevity, and robustness that
inorganic LEDs offer and are one of the main reasons that the industry has been slow to
adopt OLEDs. hLEDs, on the other hand, are both organic and inorganic and possess the
best features from both OLEDs and LEDs. Because hLEDs have many of the advantages
but face fewer obstacles than OLEDs, we have the opportunity to leapfrog OLEDs with
this technology.
Entry Strategy
We anticipate a staged entry into the display market. The goal is to co-develop hLED
display prototypes with our first customers and expand our IP portfolio. In exchange for
exclusive use of the hLED technology, our partners will help us create a complete display
prototype. The ideal target for such a partnership would offer military funding for R&D
and have little current stake in OLEDs. Such an agreement will further develop our core
technology and afford us more flexibility in crafting revenue strategies when targeting
new segments.
Stage 1: Avionics Applications
We believe the avionics display industry to be the perfect point-of-entry for hLEDs. To
capture the most from our technology, we will initially target avionics displays for
military applications. Product specifications are set by military documents, where the
emphasis ison capability rather than cost: particularly important specifications are
weight, durability, and visibility in direct sunlight. Potential customers include display
integrators such as Vuzix and Parvus. Because these customers are integrators, brand
owners, and retailers, they flatten the value chain and offer the best opportunities for
co-development partnership and military-sponsorship.
Stage 2: High-end consumer devices
After initial penetration into the display market, we plan to target luxury consumer
applications. Apple's Display and Touch Division has already expressed interest in our
technology. They have stated that we address many of the problems they experience
with potential OLED manufacturers for their small or midsized devices. Similar to Vuzix
and Parvus, Apple also takes the role of system integrator, brand, and retail, flattening
the value chain. Although they do not manufacture their displays, their engineers qualify
processes and heavily encourage their suppliers to adopt certain technologies. We
believe they will help bring us into the high-end consumer market.
Stage 3: Large screens - The final frontier
Once established in the small and midsized display markets, we will push into the
display market's final segment: large screen displays. The large screen market is
extremely attractive for hLEDs because it currently accounts for 72.3% of all consumer
display sales and has the poorest OLED market penetration. While the large screen
176
market isvery enticing, we will address this market last as it demands high-quantity,
low-margin products and a mature manufacturing process.
Sales strategy
hLEDTechnologies' sales strategy involves two steps:
First, we co-develop hLED display prototypes and enrich the IP portfolio by partnering
with several display manufacturers, particularly those with no current stake in OLEDs.
We will own the IP developed; in exchange our partners are afforded a certain amount
of exclusivity in their hLED segments. Key terms of partnership will be: exclusive rights
for the initial period in our partners' products, free of licensing charge during the second
period and licensing charge from then onwards.
Next, we focus on offering technology development services and licensing of our IP
portfolio, targeting flat panel display manufacturers, integrators, and adopters in the
relevant markets. One of our founders, Professor Karen Gleason, co-founded GVD
Corporation, which sells customized manufacturing equipment suitable for making
hLEDs. We will include sales of this equipment as part of the hLED technology
development services package. Combined with the upfront development of functional
prototypes, we are selling a full hLED display manufacturing solution. This strategy
increases the likelihood of licensees adopting hLED directly with few R&D costs, rather
than shelving our technology. In the long run, we believe that combining patent
licensing with technology development services isthe most efficient and effective way
of commercializing and populating the revolutionary display technology. This strategy
will allow us to mitigate the potential for product delays, such as those experienced by
display licensers such as Cambridge Display Technologies.
Financial Projections
The main source of revenue for hLED Technologies will be recurring IPlicensing fees and
royalties. Additional revenue will be generated from developing and supporting a supply
chain that has the capability to supply the global display markets with the materials and
services needed to manufacture hLED devices. While much of the revenue will rely on IP
licensing, by becoming the leading authority on hLED display solutions we can continue
adding value long after patent expiry. Capital expenditures and administrative expenses
are expected to be low due to the inherent cost advantage that the technology has and
the expected funding for military applications. As a result, the firm is projected to have
positive cash flow throughout much of the life of the firm, and net profit is expected to
reach $40 million by year 5.We also expect to begin to generate more revenue from
technology development and equipment services and in year 3. Given the forecasted
market for OLED technology, our model reflects an increase in royalties with time.
Financing needed and planned exit
hLED Technologies will pursue a business model that will initially focus on a few
strategic partnerships to further develop the core technology and to increase the IP
177
portfolio. hLED Technologies will own the IP developed, and in exchange, hLED's
partners will be afforded a certain amount of exclusivity in their market segment. During
this phase, hLED's strategic partners will bear the majority of R&D and some SG&A
costs. We anticipate the firm to require approximately $20 million in military funding
over the first two years.
From year 3, hLED will start to work with GVD Corporation to offer customized
manufacturing equipment, and offer technology development services and licensing for
flat panel displays. Revenues are expected to rapidly increase as our technology expands
into the larger consumer display market. This strong revenue growth will be supported
by lower costs.
There are several viable exit strategies for hLED. We could sell the business to an
existing licensing company, manufacturer or buyout firm; or take the company public
through an IPO. Historically, the most successful OLED licensors have sold their IP rights
and assets to large display integrators.
Milestones
To keep hLED technologies on track for a successful staged market entry, the following
milestones are set for the first five years:
e Year 1-Establish co-development partnership with key customers and develop hLED
display prototype
e Year 2-Obtain avionics retrofitting contracts to sell/replace > 10,000 avionics displays
*
Year 3- Establish relations with high-end display manufacturers and assist development
of small/midsize displays
*
Year 4-Three lines of high-end products using our display technology. Approach large
screen display manufacturers
e
Year 5-Assist in development of large screen hLED displays. Expect release of new
products in mid 2016.
The Team
Professor Karen K.Gleason isthe Associate Dean of Engineering for Research at MIT
and the Alexander and I. Michael Kasser Professor of Chemical Engineering. Professor
Gleason received her B.S. in Chemistry and M.S. in Chemical Engineering at MIT and her
Ph.D. in Chemical Engineering at the University of California at Berkeley. She received
both the NSF Presidential Young Investigator and ONR Young Investigators Program
awards. She has authored more than 150 publications. From 2001 to 2004, she served
as Executive Officer (Vice-Chair) of the Chemical Engineering Department and from 2005
to 2008 served as Associate Director for the Institute of Soldier Nanotechnologies at MT.
In 2001, she co-founded GVD Corporation, a technology company based in Cambridge,
MA.
178
KiranDivvela has been involved with Internet startups since 2000, starting as a cofounder of FeedMe and most recently at the venture backed social gaming startup
Dotblu. Kiran started his career at Apple after graduating with a degree in Computer
Science from the University of Michigan
Yoo Mi Hong worked as a Senior Analyst in Lehman Brothers' Global Real Estate Group,
where she performed valuation analyses and conducted due diligence on real estate
investments. She was also an Associate and Co-Founder at Principal Investment Advisor,
a real estate and distressed debt investment firm. Ms. Hong received a BA in
Computational and Applied Mathematics from Rice University and is an MBA candidate
at MIT Sloan School of Management.
Eric Lam was part of a product development team at Hewlett-Packard where he worked
on outlining and characterizing printing fundamentals for next generation inkjet
printers. He is continuing his work in researching inkjet printing applications for
deposition and micromachining as a PhD Candidate in EECS at MIT. He has two BS
degrees from the University of Washington in EE and BioE and an SM in EECS from MIT.
Hai Liu worked as an Assistant Product Manager at the Digital Media & Communications
Division of Samsung Electronics, where he specialized in consumer electronics product
development, emerging market strategies, telecom client management and
manufacturing quality control. He isan MBA candidate at MIT Sloan School of
Management, and he holds the BS and MS degrees, majored in EE, from Shanghai Jiao
Tong University and Seoul National University, respectively.
Nathan Trujillo, PhD is an MBA candidate at the MIT Sloan School of Management. Prior
to Sloan, Nathan received his PhD in chemical engineering from MIT under the
mentorship of Professor Karen Gleason and an MS in Chemical Engineering Practice.
Prior to MIT, Nathan also worked as a process engineer at Intel Corporation and for
General Atomics Corporation's nuclear hydrogen production project. He attained his BS
in Chemical Engineering from the University of California at San Diego.
179
MARKET ANALYSIS
Since there iscurrently no hLED market, we will report on the OLED market. The OLED
market is currently over $600 million. However, Display Search (a market research firm
dedicated to displays) believe that OLEDs will become a $7 billion industry by 2016.
These numbers are trending upwards. As mentioned before, the OLED market is set to
increase over 10x in a six-year period. Also, as people become more energy conscious,
we believe that trend will grow.
Currently, OLED market growth iscontingent upon the increased adoption of high-end
phones and MP3 players. Many high-end phones and MP3 players use OLEDs as a point
of differentiation because of their higher quality and lower energy consumption. Since
our technology facilitates LED manufacturers' ability to create OLEDs, we believe that
the adoption of hLED manufacturing technology will increase the demand for the
category of lower power, high contrast display technologies, which is ultimately a
substitute for LEDs.
The market opportunity is a function of a shift from an older technology (LED) to a
newer, better technology (OLED). However, since OLED is prohibitively expensive, hLED
allows LED manufacturers to leapfrog OLED to a different type of low cost, high quality
display technology.
Market Segmentation
Display Sizes
The display market can broadly be segmented by display sizes: large screens, midsized
screens and small screens. Included in the large screens category are television panels
and flight simulator screens, which typically are 24" in diagonal or larger. Flight
simulators can require displays that are even larger when mimicking the windshield.
Among the midsized displays are laptops, computer monitors, smaller television screens
and flight simulators. Finally, consumer handheld displays such as cell phones, PDA
devices and mobile media players comprise the majority of the small screens market.
Helmet displays in the military that project a virtual image to simulate large screen
displays also comprise a segment of the small screens market.
Large screens- Approximately 72.3% of sales of displays come from large screens.1 The
major LCD television makers are BenQ, TECO, Sampo, Tatung, Lite-On, AOC, Compal,
Visionbank, Phlips, Coretronics, and Albatron. These are then rebranded to Sharp,
Philips, Samsung, Song, LG Electronics, Panasonic, Toshiba, JVC, Sanyo, TTE, and Syntax.
These LCD manufacturers make up over 70% of the LCD market.
Frost & Sullivan. Market Engineering Research. World Display Driver ICs Market. <http://www. frost.com.libproxy.mit.edu>.
180
Although the majority of televisions today are made using LCD technology, major
manufacturers are split on next generation technology. Some, such as Sony, have
committed to OLED technology, although at a slow adoption rate. In an interview
conducted by Tech Radar, Sony states "The OLED TV market will not surpass the LCD TV
market within the next few years... Rather, we think it is necessary to steadily cultivate
OLED so that we can deliver new lifestyle ideas and applications that make full use of
OLED technology." They realize the value in OLED, but also accept the manufacturing
problems that need to be addressed to enable OLED technology.
Others are less enthusiastic. According to Carl Mansfield from Sharp Labs, they "do not
have any activity in this area and had no interest in proceeding with a discussion." The
main reason seems to be that television flat panel display is so cost sensitive and capital
intensive that until a disruptive technology with mature manufacturing techniques is
developed, most vendors will remain with the conventional flat panel technologies of
LCD and plasma.
In flight simulators, the top sellers are CAE, FSI, Thales, and Mechatronix. A major
manufacturer (anonymous by request) revealed that the display unit alone cost
approximately $1M: "The civil market is 20 to 40 FFS / year, let's say 200 and $400M /
year. Visual system is around $1M / FFS." Decreasing the cost of the visual system can
be interesting, but more importantly is decreasing weight, since the dynamic platform is
approximately 12 tons; OLED and OLED-like technologies can address this pain. Today,
the main technology used is liquid crystal on silicon (LCOS), a rear projection display
technology which is cost effective for large displays. OLED-like technologies have fewer
components and can be competitive here as well. Because these customers require low
quantities with high margin, it is possible to be successful in this market with a
2
prototyping lab.
Midsized screens-Midsized and small screens comprise 27.7% of total sales. 3This
segment isdominated by laptops and computer monitors in the consumer space. In
laptops, the OEM manufacturers are Quanta, Compal, Winston, ASUS, Unwill, FIC,
Arima, ECS, Clevo, Mitac, and LG Electronics. These are normally rebranded to Dell, HP,
Acer, Toshiba, Lenovo, Fujitsu-Siemens, Sony, NEC, ASUS, Apple, and Gateway. The top
ten make up over 80% of the market. The OEM manufacturers of computer monitors
are AOC, BenQ, Foxconn, Lite-On, Philips, Coretronics, Compal, Delta, Proview,
Samsung, and LG Electronics. These are then 8 rebranded to Dell, Samsung, HP, Acer,
LGE, Philips, BenQ, Viewsonic, Lenovo, SONY, and NEC DS. The top ten make up 67% of
the market.
Looking at flight simulators, each virtual cockpit requires multiple screens to display
diagnostics and controls. Similarly, their real world counterparts in avionics require the
2 iTeams Report. Massachusetts Institute of Technology. Hybrid Inorganic-Organic Light Emitting Diodes.
3Frost & Sullivan. Market Engineering Research. World Display Driver ICs Market. <http://www. frost.com.libproxy.mit.edu>.
181
same hardware. Many of the hardware manufacturers, such as Parvus, provide durable
but bulky display units. OLED displays can potentially be thin and lightweight, but
durability is still an issue. Hybrid LED displays can provide a solution to both of these
major problems. And because the market is less competitive than the consumer space,
there is more potential to compete on functionality rather than manufacturing
efficiency.4
Small screens- The handheld display market is also highly competitive, but here OLEDs
have penetrated the market much further than anywhere else. They are already being
used in many commercial devices. In 2008 for example, Nokia began requiring all of
their small screen vendors to be able to produce OLED displays. Hybrid LED is a good fit
with niche consumer applications such as the Apple cell phone and mp3 players because
they can command higher margins and afford these manufacturing costs. However,
because the technology needs to be mature enough to sell to a live manufacturer, the
technological risks are too substantial at this time.
Finally, helmet displays are the analog to handhelds for the military market. They are
generally even smaller, and project a virtual image into the eye to simulate large screen
displays at a fraction of the weight. Because they are to be worn in rugged terrain, the
most important requirements are weight and durability.
Considering each of the segments of the display market according to display size, the
large screen market seems attractive for hybrid LED because there is a large
addressable market that has experienced less market penetration by competing
technologies such as OLEDs.
Industry
The display market can also be segmented by industry. The four main industries that
purchase display systems are military, medical, consumer electronics and industrial.
Summarized below are the total market size and segmentation according to technology.
Military- The military comprises roughly 10% of sales in the display market with roughly
1,161,977 displays. DoD budget for technological development has risen drastically over
the past few years with billions of dollars added to the DoD budget for R&D
development.5
Today the flat panel display market is largely dominated by LCD panels. Much research
and engineering work is being done on OLED panels to push it as the next technological
node in displays. Hybrid LEDs provide many of the same benefits of OLEDs, and solve
some of the difficult manufacturing issues, which may allow our hybrid LED technology
4
iTeams Report. Massachusetts Institute of Technology. Hybrid Inorganic-Organic Light Emitting Diodes.
5Daniel D. Desjardins, James C. Byrd, and Darrel G. Hopper. SPIE Digital Library. Military display market: update to fourth
comprehensive edition. <http://www.spiedigitallibrary.org/>.
182
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to replace OLED as the next node altogether. Given the conditions of the market and the
relatively high cost to a display manufacturer of transitioning from the current LCD
technology to ours, we decided to pursue commercialization through targeting the
avionics industry. The industry values displays that are lightweight, durable and high
contrast, all conditions that are satisfied by the technology. In the following section we
give an overview of this industry.
The Avionics Market- The current IOLED tests have yielded parts with a brightness of
1600Cd/m2. This exceeds the brightness specification necessary for the avionics market.
The current lifetime numbers are 10,000 hours, which is not sufficient for the avionics
market. While the required lifetime number varies widely it is generally considered to
be 20,000 hours minimum, and up to 50,000 hours. Some devices have even less
stringent specification, for instance the Northrop Grumman Military Avionics MultiFunction Display has a MTBF of only 5677 hours, something that we can already
achieve. Efficiency is less important in this market, which is important as the current
research isyielding relatively low efficiency when compared to other display types.
While it seems logical that the efficiency will improve dramatically it is the one metric
6
where the current technology performs well below existing displays.
Figure 1.LCD display configuration for a Boeing 747
Displays are a critical component of airplanes, as they display vital information to the
crew. Currently, most displays are LCD. There are inherent problems with LCD in the
avionics industry, but there has never been a different technology that could compete.
The avionics demands light-weight displays with high contrast. We believe the inorganic
organic hybrid LED is a perfect technology for the avionics display industry. Low weight
is desired, as every fraction of a pound that can be removed will boost performance of
6
iTeams Report. Massachusetts Institute of Technology. Hybrid Inorganic-Organic Light Emitting Diodes.
183
the airplane. Also, high-contrast ratio is important, as airplanes will be operated both in
direct sunlight and nighttime, which require drastically different brightness levels.7
The avionics market is made up of military, commercial and private aircraft. The military
market istempting to go after, as the margins are quite high. Despite the relatively small
variety of airplanes being produced at any one time there are regular retrofits of
existing airplanes, and these almost always involve an upgrade to the displays. In
addition, there isa push to move away from analog gauges so the number of displays in
the military aircraft market isonly going to increase. With nearly 20,000 new planes in
the next 20 years, there is a feasible market for avionics displays.
Medical- The medical industry comprises roughly 5%-6% of total sales in the display
market. The market size is $329.9 million in terms of revenue and 110,499 in terms of
number of units. Typical applications are medical imaging acquisition display monitors,
diagnostic and referral display monitors, surgical display monitors and patient medical
display monitors. 9
Consumer Electronics- The consumer electronics industry is the largest with roughly
70% of total sales. An increase in the demand for digital information coupled with the
demand for portability of devices is one of the main drivers backing the race to develop
new and innovative technologies in consumer electronics. Current trends in the industry
are clear indicators of the same. The display industry has witnessed significant growth,
both technologically, as well as in terms of market volumes. Earlier, all displays were
based mainly on CRT technology, however, over the past few years LCD and plasma
displays have invaded the CRT space in a number of sectors. LCDs, owing to their low
cost, have found wide use as displays in portable devices and laptops. However, as
technological developments are continually on the rise, OLED (organic light-emitting
diode) displays are now seen to be upsetting the strong foothold that LCDs have
enjoyed so far in the display market.10
Industrial- The industrial sector comprises roughly 7%-10% of total sales with a wide
range of displays manufactured for industrial applications.
Competing Technologies
Liquid Crystal Displays (LCDs)- LCDs are still the display technology of choice for small
and midsized displays. LCDs rely on a backlight and subtractive processing of light to
produce a range of colors. Although efficient backlighting allows the technology to
utilize relatively low power, the inherent subtractive process leaves potential for
improved light efficiency. Furthermore, the subtractive process puts a limit on the
iTeams Report. Massachusetts Institute of Technology. Hybrid Inorganic-Organic Light Emitting Diodes.
Daniel D. Desjardins, James C. Byrd, and Darrel G. Hopper. SPIE Digital Library. Military display market: update to fourth
comprehensive edition. <http://www.spiedigitallibrary.org/>.
9 Frost & Sullivan. Market Engineering Research. North American Medical Display Monitors Markets. <http://www.
frost.com.libproxy.mit.edu>.
10iTeams Report. Massachusetts Institute of Technology. Hybrid Inorganic-Organic Light Emitting Diodes.
8
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darkest black that can be produced, and hence a limit on contrast ratio. LCDs comprise
roughly 90% of the market."
Organic Light Emitting Diodes (OLEDs)- To solve the two major problems associated
with LCDs as described above, much recent work has been done to enable OLEDs.
Instead of a subtractive process, OLEDs are additive. Blacks are blacker and less light is
lost due to absorption. However, problems remain with OLED technologies, and these
problems have slowed the transition from LCDs, as shown in the penetration diagram
below. OLEDs are sensitive to moisture, which complicates the manufacturing process
and inhibits high durability. In addition, the dyes no not inherently have a high lifetime.
Thus, applications with OLED displays are currently very few and concentrated in the
consumer electronics market. OLEDs comprise roughly 4% of the market.1 2
3D and Holography- 3D and holography are being adopted in the medical industry for
the use of volumetric 3D displays for specific applications. Penetration in consumer
electronics has been low and is currently limited to gaming applications. In the industrial
market, oil and gas exploration and production sectors utilize 3D visualization. 3D and
holography serve roughly 1%-5% of the total market.' 3
Multi-touch Displays- Multi-touch displays are currently available only in high-end
mobile phones and serve roughly 1%-5% of the total market. 14
In light of the market analysis and segmentation performed above, to capture the most
from our technology, we will target displays for military applications initially. Product
specifications are set by MIL documents, and emphasis ison capability rather than cost.
In particular, the important factors discussed previously are weight, durability, and cost.
Visibility in direct sunlight is also a must. Flexibility here can also be leveraged for large
displays in flight simulator applications. Potential customers include eMagin, Vuzix, and
Parvus. One reason the value chain isflatter for niche applications, is because these
companies are essentially integrators, brand owners, and retailers. Afew, including
eMagin, also own IPon materials.
After honing our product with sales and collaboration with military, we plan to target
niche consumer applications. Apple's Display and Touch Division has shown interest in
our technology. We address many of the problems they experience with potential OLED
manufacturers. Like many of the military manufacturers above, they take the role of
system integrator, brand, and retail, and flatten the value chain. Although they do not
manufacture themselves, their engineers qualify processes and heavily encourage their
suppliers to adopt certain technologies. They will help bring us into the high-end
consumer market.
11 Frost & Sullivan. Market Engineering Research. World Display Driver ICs Market. <http://www. frost.com.libproxy.it.edu>.
Frost & Sullivan. Market Engineering Research. World Display Driver ICs Market. <http://www. frost.com.libproxy.mit.edu>.
Frost & Sullivan. Technical Insights. Innovations in Display Technologies. <http://www. frost.co
m.libproxy.mit.edu>.
13 Frost & Sullivan. Technical Insights. Innovations in Display Technologies. <http://www. frost.com.libproxy.mit.edu>.
1
13
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Finally, after our hybrid LED process has penetrated the consumer market, we will
attempt to enter the commodity display market. Here, the top three FPD integrators are
Samsung, LG, and AUO. Samsung and LG brand some of their displays, but for the most
part FPD integrators are at the bottom when it comes to margin. High quantities make
up for these low margins, so cost efficiency is most important. By this stage, we hope
our manufacturing process will be tuned to be competitive with the state of the art,
while our technical specifications remain superior.
Competition and Competitive Advantage
Initially, hLED Technologies seeks to forge partnerships with avionic and military display
manufactures. Such an agreement will help develop our core technology and afford us
more flexibility in crafting revenue strategies when targeting new segments. We will
likely encounter competition at each stage of market entry as most of our targets are
current or prospective OLED customers. The main competitors are categorized into four
areas involving OLEDs: developers for avionics and military displays, materials
developers, commodity display manufactures, and general lighting developers.
Avionics/Military Applications
eMargin- eMargin is a company that develops OLED microdisplay& virtual imaging
technologies. While having high-end 3D display visors for consumers, their primary
business has been in the development of military applications. eMargin licenses their
OLED technology from Eastman Kodak and has developed additional IP on materials.
They were recently awarded $6M towards the development of a ultra-high resolution
OLED microdisplay for the US Army. They reported 2009 Q3 revenue of $6.1M.
Given the additional IP eMargin has already developed for their OLED products, it is
unlikely that they will readily adopt hLED technology and can be seen as a direct
competitor to our efforts to form partnerships for avionics & military applications.
eMargin's has a competitive advantage in the military markets because they have been
first to develop OLED products for the military and have been continually broadening
their portfolio. However, eMargin epitomizes the OLED market: eMargin has needed to
develop a lot of additional processes in order to overcome the issues with the yield and
stability of their OLEDs. Our advantage over eMargin isthat our technology is inherently
more stable and does not require as much supporting processes to build a viable
product.
QD Vision Inc.- QD Vision is arguably our closest competitor our hLED technology also
uses quantum dots (namesake for QD Vison). Founded in 2004, QD Vision's purpose is to
manufacture "LED technologies for consumer electronics products, flat-panel displays,
electronic signage, solid-state lighting, and national security applications". Despite
having over 30 patent applications around using quantum dot technology, little is known
about their product development strategies. Last year QD Vision released its first
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product which was a QD-LED light bulb intended for consumer usage. This product was
developed in partnership with Nexxus Lighting Inc. and future products have not been
disclosed. As QD Vision is approaching the market from the other end of the value chain,
they are not seen as direct competition in the near future.
Despite only having one product, QD Vision was awarded $775k from the US Army Small
Business Innovation Research Phase Il Grant as part of its Night Vision and Electronic
Sensors Directorate. In addition to the grant, QD Vision has raised $13M in financing
within the last year. While QD Vision has a significant advantage in financing, their lack
of products over 5 years potentially suggests poor market analysis or significant issues
with R&D, which hLED Technologies can capitalize on. Patent encroachment isanother
serious risk we might encounter when competing with QD Vision-- this will need to be
monitored.
Materials Development
DuPont- DuPont started developing materials and processes for OLEDs in 1993 and is
currently one of the largest supplier of OLED materials and processes for OLED displays.
As one of the leaders in OLED technology, DuPont is one of our major competitors.
DuPont is currently addressing several of the issues with OLED manufacturing: using
solution-based processes to reduce process material costs and reducing the number of
patterned layers to increase throughput & yield. In addition to process improvements,
DuPont is continually improving their OLED materials: in 2009 DuPont introduced their
3rd-generation OLED materials, indicating significant increases in OLED lifetimes.
DuPont operates by selling their OLED components and licensing the process technology
to display manufacturers.
Merck KGaA- Merck is a material's company with short term and long-term strategies
for OLED materials development. In 2009 they made $7.7B in revenue, representing a
2%sales growth. Merck has a leading market position in blue singlet materials and is
strongly focused on developing highly efficient emitting materials for next generation
OLEDs. They are developing their IP portfolio to include materials for the hole-injection
layer--namely small molecules and evaporable materials. Merck acquired all of OLED-T's
assets in 2008 to further expand their IPin electron transport and phosphorescentemitting materials for OLEDs. Their long-term plans are to develop ink-jet processable
OLED materials, to help their customers achieve reduced manufacturing costs. As a
material supplier, they work in close cooperation with key customers to deliver
continuous material improvements to achieve the customer's targets. The identities of
these customers are protected under NDA, but are likely high-end display
manufacturers.
Since Merck's business ison the extreme end of the value chain, it will be worth
investigating partnership development opportunities in order to better target a broader
display market.
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Display Technology
Sony- Sony is one of the world's largest consumer electronic companies with annual
revenues exceeding $79B. They were late in entering into the LCD market, and in 2008
they announced that they would invest $200M on OLED production lines for midsized
and large-sized panels. They have developed a proprietary packaging process that allows
them to seal off the OLEDs from the atmosphere, increasing the lifetime of the display.
Currently, an 11" OLED display sells for $2500. Unless Sony can significantly reduce their
manufacturing costs, they will unlikely penetrate the niche avionics display market
anytime soon.
Samsung- Samsung is pursuing OLED development efforts through their wholly owned
subsidiary, Samsung Mobile Displays (SMD). In 2005 SMD established a patent license
agreement with Universal Display Corporation in order to integrate OLEDs into SM D's
active-matrix display products. They are currently the largest supplier of passive-matrix
OLED displays in the world. Color OLED displays for the mobile phone display market are
manufactured using both active matrix OLEDs (AMOLED) and Passive Matrix OLEDS
(PMOLED). SMD isthe largest supplier of passive-matrix OLED displays in the world and
their 3" AMOLED panel isincorporated into mobile phones, MP3 players and other
mobile devices. For future OLED applications, SMD pursuing large panel displays and
flexible/transparent displays. For example, they are expected to release a 55" OLED
display by 2015.
State of the art SMD OLEDs have an expected lifetime at 90% emission of about 15,000
hours. They minimum required lifetime for avionics displays is about 35,000 hours.
Therefore, SMD OLED will unlikely pose a threat until they can increase their material
stability and extend their lifetimes.
LG Display- LG Display is a large maker of displays for TVs, computer screens and mobile
devices with a primary focus on AMOLED displays. In December of 2009, LG Display
bought Kodak's OLED division for $100M, giving LG an incredibly versatile OLED IP
portfolio. Currently, LG Display manufactures small OLED displays for mobile phones and
similar devices solely for Korean market. The capacity is limited at 7k sheets/month,
which is equivalent to 200K 3" screens. LG Display has announced that their 15" Active
Matrix OLED (AMOLED) display will be released in Europe for 1999 Euros by May 2010.
They have forecasted that the large screen displays (> 30") from their new 5G AMOLED
plant will be released by 2013.
General Lighting Applications
Mitsubishi Chemicals- In2009, Mitsubishi Chemicals have paired up with UDC to
develop new solution-based OLED materials. Additionally, they recently paired with
Pioneer to enter the OLED lighting market. Their lighting prototype has not been
demonstrated and is scheduled for April 2010.
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Philips- Philips is the world's largest supplier of LED based lighting has been developing
their technology capabilities in OLED lighting since 2001. In 2008 they generated $7.1B
in lighting revenues, representing 17% sales growth. Much of this growth was driven by
the acquisition of smaller solid-state LED companies. In 2007, they boosted their sales
growth 11% by acquiring Boston-based Color Kinetics. Their acquisition of Lumileds in
2005, made them a leader in high-power LED dyes, and the recent acquisition of TIR
Systems provided them with lines of fully-integrated Solid State Lighting (SSL)-modules.
While they have active research in OLED technology, most of their research is dedicated
to their Lumiblade line of lighting panels.
As these products almost exclusively target lighting applications, they would likely not
compete against our hLEDs in the avionics display segment. Philips manufacturing
process competes on homogeneity of emission over the complete surface of a device
and not on device resolution, which is an essential component of display manufacturing.
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SALES & MARKETING
Overall Market Strategy
hLED Technologies' sales & marketing strategy involves two stages:
Stage 1: Avionics Applications Co-development
We plan to co-develop hLED display prototypes and enrich our IPportfolio by partnering
with avionics display manufacturers. The ideal target for such a partnership would offer
military funding for R&D and have little current stake in OLED technology. Moreover,
avionics demand high contrast, lightweight displays, making hLED technology a perfect
fit. A co-development agreement will further develop our core technology and afford us
more flexibility in crafting revenue strategies when targeting new segments. Working
with an established avionics display manufacture will allow us to quickly incorporate the
hLED technology into a working prototype. According to the Research and
Development Council, a common contractual approach for the relevant IP created by
either or both parties during the co-development alliance is that "one party retains
complete IP ownership and grants licenses, limited according to field of use, to the
other party." We will own the IPdeveloped in creating the prototype; in exchange our
partners are afforded a certain amount of exclusivity in their hLED segments. The key
terms of the partnership will be: exclusive rights for the initial period in our partners'
products, no licensing charge during the second period, and licensing charge from then
onwards.
Stage 2: Patent Licensing and technology development services
Next, we will target consumer display manufacturers, integrators, and adopters in the
relevant markets and offer display technology solutions and licensing of our IP portfolio.
The display technology solutions will include: customized equipment, installation
services, and ongoing process support. One of our founders, Professor Karen Gleason,
co-founded GVD Corporation, which sells customized manufacturing equipment suitable
for making hLEDs. Having access to this organization will enable us to offer customized
manufacturing equipment as part of our hLED technology suite. Combining the upfront
development of functional prototypes with the on-site assistance of our engineers, will
we are selling a full hLED display manufacturing solution. This strategy increases the
likelihood of licensees adopting hLED directly with few R&D costs, rather than shelving
our technology. In the long run, we believe that combining patent licensing with
technology development services isthe most efficient and effective way of
commercializing and populating the revolutionary display technology. This strategy will
allow us to mitigate the potential for product delays, such as those experienced by
display licensers such as Cambridge Display Technologies.
After initial penetration into the avionics applications, we plan to target luxury
consumer applications. As previously mentioned, Apple's Display and Touch Division has
expressed interest in our technology. Similar to Vuzix and Parvus, Apple also takes the
role of system integrator, brander, and retailer, flattening the value chain. Although
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they do not manufacture their displays, their engineers qualify processes and heavily
encourage their suppliers to adopt certain technologies. We believe they will help bring
us into the high-end consumer market.
Stage 3: Large screen displays
Once established in the small and midsized display markets, we will push into the
display market's final segment: large screen displays. While the large screen market is
very enticing, we will address this market last as it demands high-quantity, low-margin
products. We could face stiff competition from Sony, Samsung, and LG as all three
manufactures have invested substantial capital into OLED technology and will likely
resist adopting our technology initially. Other large screen vendors such as Sharp have
expressed that until a disruptive technology has mature manufacturing techniques, they
will continue to focus on conventional LCD displays. Thus, it would be difficult to
compete without first establishing ourselves in other display market segments and
maturing our manufacturing processes.
Pricing
The pricing of patent licensing and technology development services include various
options:
Royalty
Lump sum
Licensing + tech development services
Patent licensing only
Cost of tech development services+ 25%
5% of the sales
Projected 10-year royalty
The royalty rate is based on a representative pricing scheme for similar services in the
OLED space, which can usually range from 3-6%. A lump sum payment of royalties (for
sales projected over a 10 year period) will be considered on a case-by-case basis. This
will provide us with short-term cash flow, but will require that we reduce the royalty
rate.
Technology development services are a crucial to the successful uptake of the hLED
technology by new customers. At this stage, extensive knowledge of the process and
components isessential, at an engineering level, and operations level. Customers will
heavily rely on these services during the initial installation of the system, but will also
require recurring services to maintain, repair, and/or upgrade the production line. The
customer will cover the cost of delivering the services, including engineer's salary,
travel, and overhead. An additional 25% markup represents the margin. This is a
standard margin rate for consultants.
Customized equipment prices are set by GVD, however we will sell the equipment at a
10% markup as a convenience (finder's) fee. Purchasing and/or leasing arrangements
are subject to GVD's protocols.
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Sales Tactics
Our sales plan will include the following phases to secure the desired partners in
avionics and military displays sector.
* Contact potential co-development partners through direct sales (emails, calls
and visits), public relation companies or personal networks. Set up meetings and
invite key inventors, scientists and professors from MIT to add credibility.
*
Conduct negotiation with partners on terms of co-development agreement.
These discussions usually involve an alliance advocate at the executive level,
director-level cross functional representatives, and a dedicated technical staff.
Determine the project timelines, joint-team dynamics and communication
channels based on mutual benefits. Nominally, the "exclusive rights" and "free of
licensing charge" periods will last four and two years, respectively.
Sales at the licensing phase will follow several procedures to ensure a growing source of
revenues:
e
Develop dedicated sales force and post-sales service team.
e
Determine deal structure, licensing fees and licensee targets. Both lump sum and
royalty payment will be considered.
e
Reach potential licensees through viral marketing campaigns by demonstrating
successful hLED prototypes in our partners' particular display segments.
Illustrate prototypes at exhibitions and conferences such as the Consumer
Electronics Show (CES) in Las Vegas. Set up meetings with interested customers.
*
Conduct negotiation with licensees on terms, conditions and licensing technical
support. Sign win-win agreements, finalize technology transfer and generate
revenues.
e
Build on success and penetrate more display segments on top of established
reputation.
*
Table 1 illustrates the timeline of market expansion.
2011
2012
2013
2014
2015
2016
Avionics Displays
High-end Devices
Flat Screens
Table 1. Sales & Marketing Penetration Timeline
Sales Force Growth
The avionics co-development stage requires virtually no sales force. The founding team
will be mainly performing the roles of salesmen during this period. The sales force will
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be established once a fully functional display prototype has been developed. The
number of high-end device display manufactures and adopters are limited. As such, we
plan to hire 5 sales representatives to target the small- and mid-sized display
manufacturers. They will focus primarily in engaging in discussions with the directors for
new business development within these companies. When expanding into flat screen
display market, we double the number of sales reps to 10. The compensation of sales
force includes annual base salary ($100,000) and commission (5%of the deal value).
The technical nature of the hLED products requires that training become a primary
component of the sales recruiting process. Prior to engaging in sales, each sales person
will be paired with a technical services engineer. They will accompany each other on at
least 2 service calls/installations, so that the sales person can be familiarized with the
services we are offering.
Branding & Promotion
The hLED brand represents a disruptive innovation for the display industry. We license
technology and provide display technology solutions, which will improve performance
and significantly reduce manufacturing cost of LED applications. The first promotion
channel of our hLED brand is a website including company introduction, successful
licensee cases and deal explanation. The communication platform between academy
and industry such as papers, journals, seminars, workshops and conferences are other
channels to promote hLED brand. Public Relation companies will be another choice to
spread hLED names over the display industry.
Additional brand awareness will be generated from stage 2 onwards. Similar to how
Intel Inside® publicizes that a product contains an Intel chipset, every product with our
technology will state "Illuminated with hLED". This product stamp requirement will be
outlined during the initial licensing agreements.
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TECHNOLOGY & PRODUCT OFFERING
Product Description
The hLED technologies product offering represents a full display manufacturing solution
for display integrators and manufacturers. hLED's revolutionary and proprietary device
architecture allows manufacturers to produce mechanically flexible and chemically
robust displays for a variety of applications. Our in-house expert engineers will evaluate
a customer's display manufacturing capabilities, and develop a customized strategy to
achieve scaled hLED display manufacturing. These strategies will offer:
e Customized process recipes and channeling of chemical resources
*
Development of custom-built manufacturing equipment (with GVD)
e
Process milestones that best leverage the licensed IP
Throughout the life of the licensing agreement, customers will have access to hLED
engineers to support continuous process improvement and equipment customization.
The combined access to hLED Technology's IPand engineering expertise provides
customers with a turnkey solution that will minimize their time to full-scale operation.
How does hLED technology work?
These hLED devices represent the pixels, which form the basis of a display. Our patentpending technology (Figure 1) has similar device architecture to OLEDs. In OLEDs, an
organic emissive layer is sandwiched between two conducting layers. When a voltage is
applied across the conducting layers, two charged species (electrons and holes) combine
in the emissive layer to release a light photon. Typical OLED devices are comprised of
unsaturated organometallic synthetic compounds. Because the unsaturated bonds are
susceptible to degradation by air and moisture, OLED devices are typically manufactured
in ultra-high vacuum environments (<10e-6 Torr) and require bulky packaging to protect
them.
The key difference between OLED and our hLED technology is our emissive layer uses
inorganic quantum dots. Because the layer is inorganic, it is more robust, able to
withstand conditions that ruin their OLED counterparts, and can be manufactured using
only a mild vacuum (~1 Torr). The increased robustness enables significant cost
reductions because we do not need the costly additional equipment, processing, and
packaging that OLED manufacturing requires. These savings can be on the order of
~$100M-$1B per facility when considering high volume manufacturing processes.
When compared to traditional LCD displays, hLEDs will use many of the same device
components (Figure 2): transparent upper electrode, transparent ITO lower electrode,
thin-film transistor, glass substrates, and display chassis-while eliminating the need for
a backlight, polarizer, and LCD array. Thus, the hLED process can lead plug into an
existing LCD display process and possibly lead to a net process simplification.
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Finally, the conducting layer consists of a conformal vapor-deposited conducting
polymer. This layer isdeposited using a proprietary process pioneered in the Gleason
laboratory. The conducting polymer is essential to the operation of the hLED and adds
increased device robustness as it patches cracks that can form in the relatively brittle
ITO anode upon mechanical flexing.
Anod on Gm
LIGHT
Figure 2. Traditional LCD display (left) and hLED device architecture (right)
Intellectual Property Strategy
hLED Technologies will pursue a business model that will initially focus on strategic
partnerships to further develop the core technology and to increase the IPportfolio.
Once prototype displays are developed, we will leverage the full range of our IPto
generate revenue.
As our manufacturing process begins to mature we will possess a set of process recipes
that are optimized for aspecific customer's needs. While generic process will be fully
disclosed to customers according to licensing agreements, it will best serve hLED
Technologies to keep certain process recipes as trade secrets, provided there is no
conflict with the terms of original co-development agreements. These decisions will be
made on a case-by-case basis as seen fit by hLED's lead R&D engineer and executive
team. GVD will exercise any decisions regarding IPstemming from customized
manufacturing equipment.
Because hLEDs core technology was developed at MIT, we will apportion revenues
directly related to this IPaccording to the MIT TLO licensing and royalty agreement.
Technical Risks
To date, functioning red hLED prototypes have been demonstrated. Red, green, and
blue devices are required to form a fully functional display. While the chemistry for
creating devices remains identical regardless of the color, certain performance issues
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can arise that are color-dependent. For example, the luminous intensity of blue
quantum dots can be quenched if too many linker molecules are attached to it.
Therefore, special attention must be directed towards these chemistries when
optimizing device recipes for blue and green hLEDs.
Much of hLED's value is drawn from the chemical stability compared to OLEDs. While
current hLED devices have already achieved lifetimes of greater than 10,000 hours at
room temperature, avionics applications require lifetimes greater than 15,000 hours.
Furthermore, in avionics applications these devices will be subjected to hostile
environments. Therefore, we need establish firm benchmarks surrounding operating
temperatures, pressures, humidity, cycle times, impact resilience, from which we can
develop additional stress tests for our devices to determine accurate lifetime values.
To date, hLED devices have been structured as a passive matrix. In order to achieve
optimal switching speed and display contrast, OLED devices have been integrated into
displays using active matrices. Therefore, we wish to incorporate active matrix design in
future generations of hLED devices. While the thin-film technology for active matrix
device isvery well established, we must be thoughtful in incorporating these processes
into our hLED device process scheme.
Development Resources
Human resources will comprise hLED Technologies most valuable asset. The
monetization of our value proposition will hinge heavily on our ability to properly
balance in-house expertise with our technological and intellectual resources. The
essential resources will vary depending on the stage of hLEDs development. Specifically,
while developing a prototype display during the initial co-development stage we will
require:
* 1 PhD chemist to lead quantum dot chemistry development
*
1 PhD chemical engineer to drive the development of conducting polymer layers using
GVD corporation's tools
*
1 PhD engineer (materials, mechanical or chemical) to specialize in integrating the
manufacturing process with inkjet printing
e
1 MS level electrical engineer to lead the active matrix device integration
In our second stage of development we will target high-end devices. By this stage, our
engineers would have developed significant competencies involving the hLED process
and can support the technology service thrust of the product offering. The integration
engineers will shift their focus to technology development services that target the highend market while the conducting layer engineer and chemist will drive our in house R&D
effort. We will hire on an additional two MS level engineers to support the technology
development services for high-end devices. The two senior engineers will be responsible
for training the new engineers in their new role. We will iterate through this process as
we move forward in targeting large-screen display applications.
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We anticipate the R&D expenses of $8M and $12M as part of our first and second years
of staged development, respectively. These figures cover:
e Salary for 1 MS level engineer $180-$200K/engineer
e
Salary for 3 PhD level engineers $200-$220K/engineer
e
Lodging, travel and meal expenses for on-site co-development
*
Equipment in R&D Phase: customized GVD reactors, process chemicals, characterization
equipment, inkjet apparatus, commercial scale gold sputtering tool, active matrix TFT
elements, logic systems/softwa re/packaging for prototype, and electrical testing
equipment
R&D over the first couple of years is expected produce a fully functional display
prototype, and should be higher than for subsequent years. From year 3 onward we
anticipate ~$1M in annual R&D expenses. This will cover salary for two engineers, a new
GVD reactor, and $300K for additional process innovations.
Product Development Timeline and Milestones
Figure 3 contains a timeline for our various stages of market entry. To keep hLED
Technologies on track for a successful staged market entry, the following milestones are
set for the first five years:
e Year 1- Establish co-development partnership with key customers and develop hLED
display prototype
e Year 2- Obtain avionics retrofitting contracts to sell/replace > 10,000 avionics displays
e Year 3 - Establish relations with high-end display manufacturers and assist development
of small/midsize displays
*
Year 4 - Three lines of high-end products using our display technology. Approach large
screen display manufacturers
*
Year 5 - Assist in development of large screen hLED displays. Expect release of new
products in mid 2016.
2011
Avionics Displays
2012 1
2013
2014
High-end devices
2015
2016
Flat screen displays
beyond
General Lighting
Figure 3.Timeline for various stages of market entry
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MANUFACTURING, SERVICES, & LOGISTICS
Manufacturing & Distribution
As we are a company focusing on providing a technology solution for display
manufacturers, our primary products are the processes and techniques needed to
manufacture hLED displays. The maturation of our core processes and techniques will
be done during the co-development phase. We will subsequently continue expanding
our patent portfolio and refining our processes in-house. Our processes will focus on
using off-the-shelf chemicals to reduce the amount of physical products we have to
manufacture.
In addition to our primary products, we will also offer the customized tools required to
manufacture the hLED displays. These tools include the QD printing system, metal
sputterer, and conformal deposition tool. Most of the tools will be acquired via third
parties and be modified in-house. The exception to this isthe conformal deposition tool,
which will be manufactured & customized by GVD. Because there are relatively few
display manufacturers, the tools will be made-to-order and subsequently directly
shipped to the customer.
Typical manufacturing and distribution of our tools will go as follows:
1. Trained engineer will visit the customer's facilities and assess their capabilities.
2. The engineer will correspond will GVD and craft a strategy to deliver the
customized conformal deposition tool.
3. While the GVD tool is being manufactured (~6 months), the remaining tools are
ordered, and customized in-house to meet customer's capacity requirements.
4. Tools are freight shipped to customers and the trained engineer installs tools
upon delivery.
Service
Under the terms of recurring technical support, we will retrofit & repair equipment
components as needed. The GVD deposition tool falls under their warranty agreements
and will subsequently be maintained by their personnel. Naturally, we will provide
technical support & consultation should there be any problems and/or the customer
wishes to install more hLED manufacturing lines.
Logistics
During the co-development phase, we expect to have a small lab facility for some R&D.
Most of our R&D is to be conducted at our partner's facilities. As we move out of the codevelopment phase and into the high-end consumer device phase, we will acquire a
small manufacturing facility. This will be used for customizing the manufacturing tools
mentioned above and serve as short-term storage of said tools while the orders are
being completed. In the final phases, we will upgrade from the small facility to keep up
with demand. Because there are relatively few display manufacturer facilities, we do not
foresee the need to invest in large-scale production of these customized tools.
198
Because suppliers of the stock tools generally target the semiconductor industry, we do
not need to worry about our suppliers keeping up with our demands. Our main
bottleneck is GVD because they are a relatively young company and their facilities are
also limited. This, however, is not a major concern because they are planning on
expanding to a new facility in South Carolina to increase their throughput.
While we're producing a small amount of physical goods, we are primarily a knowledge
provider. As such, the growth of our company's core capabilities will scale with human
resources. With our processes and techniques maturing, we will establish extensive
training guidelines and increase the MS to PhD ratio hired (~5:1). In the high-end
consumer device phase, we will upgrade to a medium-sized lab facility and leverage inhouse R&D for continuous expansion of our IPportfolio.
199
FINANCIALS & OWNERSHIP
This section outlines the financial projections and ownership structure for hLED
Technologies. A financial summary is provided, followed by a detail analysis of revenues,
cost, financial controls and ownership allocation.
The following analysis is intended to give the investor a better sense of how hLED
Technologies will be managed by giving transparency into operating and financing
decisions, as well as intended distribution of owner's equity.
Company Structuring
hLED Technologies will be incorporated as a CCorp. Although we anticipate 100% of the
equity to be held by the founders and potentially some key employees (except for the
equity venture capitalists will receive for funding), we wanted to allow flexibility in
terms of additional external funding, should the need arise, including potential IPO. We
may establish subsidiaries depending on business needs.
Financial Summary
Income Statement (Numbers are inthousands)
hIy
Technologies Income Statement Summary
2011
2012
2013
2014
2015
2,100
4,200
-
-
25,704
6,209
16,500
48,413
6,426
41,987
50,000
8,279
22,000
80,279
12,500
67,779
License Fees and Royalties
Tech Services & Developnent
Equipnent and Supplies
Total Reienue
Cost of Sales
Gross Profit
-
-
2,100
525
1,575
4,200
1,050
3,150
13,440
4,140
11,000
28,580
3,360
25,220
Research and Developnrnt
SG&A
Total Operating Expenses
Profit before Interest and Taxes
Interest Expense
7,548
920
8,468
(6,893)
(1,240)
11,048
1,060
12,108
(8,958)
(2,960)
1,048
2,830
3,878
21,341
(2,960)
1,048
3,470
4,518
37,469
(2,960)
1,048
4,170
5,218
62,561
-
7,469
13,114
21,896
Taxes Incurred
-
-
200
Balance Sheet
hLD Technoloes Balance Sheet Summary
|
CurrentAssets
Cash
Accounts receivable
Inventory
Total current assets
HxedAssets
Long-term investments
PP&E
(Less accunilated depr)
Intangible assets
Total fixedassets
Other Assets
Deferred income tax
Total Other Assets
CurrentUabilities
Accounts payable
Income taxes payable
Acrrued salaries and wages
Total current liabilities
Long-term Liabilities
Long-termdebt
Deferred income tax
Total long-term liabilities
2011
2012
2013
2014
2015
517
578
12,050
34,085
38,469
517
578
12,050
34,085
38,469
7,500
(600)
18,500
(2,080)
19,500
(3,640)
20,500
(5,280)
21,500
(7,000)
6,900
16,420
15,860
15,220
14,500
0
0
0
20,911
23,079
43,990
25,247
29,582
33,918
25,247
29,582
33,918
15,500
37,000
37,000
37,000
15,500
37,000
37,000
37,000
50
50
50
Owner's Equity
Owner's investment
Other investments
Retained earnings
Total owner's equity
(8,133)
(8,083)
(20,052)
(20,002)
(9,140)
(9,090)
12,255
12,305
52,919
52,969
TotL1 ILiablihties and s/L
7,117
60,988
~3.
7,8 7
S6.887
~
50
50
201
...............
...........
.
Cash Flow Statement
bhiI Technologes CFStatement S um
Net incomne
Adjustments to reconcile NI to NC
Increaseminreceivables
2011
2012
2013
2014
(8,133)
---
(11,918)
10,912
-
-
21,395
-
600
1,480
1,560
20151
40,664
-
1,640
1,720
Net CF from Operating Activities
(7,533)
(10,438)
12,472
23,035
42,384
Purchase of equipments
Net CF from Investing Activities
(7,500)
(7,500)
(11,000)
(11,000)
(1,000)
(1,000)
(1,000)
(1,000)
(1,000)
(1,000)
Founders' equity
Net borrowings
Repayment
Net CF from Financing Activities
50
15,500
21,500
-
-
(37,000)
(37,000)
11,472
22,035
4,384
Depreciation expense
Net Increase in Cash
15,550
21,500
517
62
Financial Assumptions
Revenue- In our revenue forecast, we estimated the license fees and royalties based on
the projected addressable market for OLEDs and projected the market share for hLED.
Market data shows that there will be a $10 billion addressable market for OLEDs by
2015. Currently there is approximately a $1 billion market for OLEDs with the projected
CAGR for next year being approximately 40%. Therefore, the estimated addressable
market for OLEDs in 2011 is$1.4 billion (this is shown in the following chart under
"Addressable Market"). We estimated our market share to be 3%based on the fact that
we will be targeting the avionics market and the total market for military is
approximately 10% of the total display market. We projected a gradual YoY increase of
the addressable market to $10 billion by 2015 and increased our market share to 10%.
We assumed a 5% licensing fee to derive the total license fees and royalties to be
received by hLED Technologies. However, given the forecasted market, our royalties
should increase with time.
For technology services and development, we projected 10 clients by 2013, 15 by 2014
and 20 by 2015. We assumed an average of 2 services performed per year per client. We
determined the salary based on the assumption that the personnel would spend an
average of 5 days per service. The travel expense includes airfare, hotel and meals for
the days of service, and we assumed average of $5,000 per service in service-related
products and infrastructure for other expenses. We assumed 25% markup, which is
similar to providing consulting services. The reason that we're starting the technology
services business in 2013 is because we're assuming that we will have a partner help
202
develop the technology, fund us and have an exclusive license on the technology for the
first couple years. Then after the exclusive expires we can go out to other companies
and sell the technology and services associated with it.
For equipment and supplies, for simplicity's sake, we assumed packaged equipment and
supplies per site/client of $1 million with the number of clients projected above. We
assumed 10% markup for customization.
Rewnue Forecast
2011
License Fees and Royalties
Addressable Market
YoYincrease
Market Share
Marketfor hLED
Subtotal
1,400,000
40%
3%
42,000
2,100
2012
2013
2014
2015
2,100,000
50%
4%
84,000
4,200
3,360,000
60%
8%
268,800
13,440
5,712,000
70%
9%
514,080
25,704
10,000,000
75%
10%
1,000,000
50,000
20
16,438
20
100
30
24,658
30
150
40
32,877
40
200
4,140
6,209
8,279
1,000
10
1,000
15
1,000
20
Tech Services & Dewlopment
# of services performed
Salary
Travel
Other expenses
Subtotal
-
-
Equipment and Supplies
Price of equipmentper client
# of clients
Subtotal
Total Sales
-
-
11,000
16,500
22,000
2,100
4,200
28,580
48,413
80,279
Because licensing fee isthe major source of revenue, we performed sensitivity analysis
on the addressable market and market share. As shown below, our sensitivity analysis
confirmed that our assumptions are fairly conservative.
203
.
18,727
19,214
19,702
20,189
20,677
21,164
21,652
22,139
22,627
23,114
23,602
...
..........................
....
....
.
21,164
22,139
23,114
24,089
25,064
26,039
27,014
27,989
28,964
29,939
30,914
26,039
27,989
29,939
31,889
33,839
35,789
37,739
39,689
41,639
43,589
45,539
23,w
25,064
26,527
27,989
29,452
30,914
32,377
33,839
35,302
36,764
38,227
28,477
30,914
33,352
35,789
38,227
40,664
43,102
45,539
47,977
50,414
52,852
30,914
33,839
36,764
39,689
42,614
45,539
48,464
51,389
54,314
57,239
60,164
33,352
36,764
40,177
43,589
47,002
50,414
53,827
57,239
60,652
64,064
67,477
35,789
39,689
43,589
47,489
51,389
55,289
59,189
63,089
66,989
70,889
74,789
Cost of Sales-Our primary cost of sales is the royalty that we would have to pay to MIT's
Technology Licensing Office (TLO). We assumed 25% based on the average figure from
start-up companies that commercialized technologies developed at top universities, but
it would depend on what we negotiate with the TLO. We could also explore the option
of buying out the patent, in which case our initial costs would increase.
Cost Forecast
License Fees & Royalties to MIT
Revenuefrom Licensing
Subtotal
Total COGS
2011
2012
2013
2014
2015
2,100
525
4,200
1,050
13,440
3,360
25,704
6,426
50,000
12,500
525
1,050
3,360
6,426
12,500
Operating Expenses- We anticipate the R&D expenses to include equipments in the
R&D phase, including customized GVD reactors, process chemicals, characterization
equipment, inkjet apparatus, commercial scale gold sputtering tool, active matrix TFT
elements, logic systems/software/packaging for prototype, and electrical testing
equipment. In addition, there will be lodging, travel and meal expenses for on-site codevelopment. Including salaries for R&D personnel, we anticipate the expenses for R&D
to be approximately $8 million and $12 million in the first and second years.
R&D over the first couple of years is expected to produce a fully functional display
prototype and should be higher than for subsequent years. From year 3 onward we
anticipate approximately $1 million in R&D expenses, including salaries for R&D
personnel. This will cover a new GVD reactor and $300K for additional process
inventions. Our funding will come from the partnership we develop the technology
with. This isalso what "On-site co-development" refers to in the expense forecast
below.
The assumptions for salaries are listed in the next sub-section. We assumed rent of
$40,000/year for about 2000 sq. ft. of office space in the outskirts of Boston, such as
Waltham (approximately $20/sq.ft.), for the first two years. From year 2, we assumed
3,000 sq. ft. of office space for $30/ sq. ft. and 10,000 sq. ft. of R&D and laboratory
204
38,227
42,614
47,002
51,389
55,777
60,164
64,552
68,939
73,327
77,714
82,102
space for $100/sq. ft. We assumed standard legal and accounting fees as well as travel
expenses, with steady growth in the final three years as the business grows bigger.
Expense Forecast
2011
2012
2013
2014
2015
48
7,500
48
11,000
48
1,000
48
1,000
48
1,000
7,548
11,048
1,048
1,048
1,048
480
620
1,240
1,680
2,180
40
40
1,090
1,090
1,090
300
100
300
100
300
200
400
300
500
400
920
1,060
2,830
3,470
4,170
8,993
13,158
7,238
10,944
17,718
R&D
On-site co-development
Equipment
Subtotal
SG&A
Salaries
Rent
Legal & accounting
Travel
Subtotal
Total Sales
Salary- The five founding members of the company will initially comprise the sales &
marketing, G&A and production personnel. The five founding members have agreed to
receive half the salary in the first year to free up cash for other expenses. We will hire
four personnel for the first and second years of staged co-development, including 1 MS
level engineer at the cost of $75-$80K/engineer and 3 PhD level engineers at the cost of
$95-$100K/engineer. The salary for these 9 employees for the first year will be
$480,000.
We expect a dramatic growth in the number of people required after year 2 as we
attempt to expand our operations beyond the avionics market. We also expect the
average salary per person to grow as our business becomes larger and more
sophisticated.
Other assumptions that are inherent in the projection are:
e
Average salary includes employee tax
e
Sales and marketing hiring and wages are based on estimates outlined in that section of
our business plan.
e
R&D hiring and wages are based on estimates outlined in the Technology section of our
business plan.
*
There are only a few people on staff because we assume that we will be able to utilize
the resources of our partner company.
205
Personnel Plan
2011
2012
2013
2014
2015
Sales & Marketing Personnel
People
Average per Person
Subtotal
2
20
40
2
40
80
4
70
280
5
80
400
7
90
630
G&A Personnel
People
Average per Person
Subtotal
2
20
40
2
40
80
4
70
280
6
80
480
7
90
630
R&D Personnel
People
Average per Person
Subtotal
4
95
380
4
95
380
4
95
380
4
95
380
4
95
380
1
20
20
2
40
80
5
60
300
7
60
420
9
60
540
9
10
17
22
27
480
620
1,240
Technical Support Personnel
People
Average per Person
Subtotal
Total People
Total Expenditures
Payroll
1,680
2,180
Interest Expense- We assumed a conservative interest rate of 8% (approx. 5% premium
over risk-free rate) for the interest expense to be incurred from government loans for
the initial three years.
Depreciation- We assumed straight-line depreciation with salvage value of 20% of
purchase price and useful life of 10 years.
Tax-We anticipated tax expenses to be approximately 35% of earnings before tax.
However, this is a conservative assumption given that the IRS's tax rate schedule varies
from 15% to 35% of taxable income for most corporations depending on the taxable
income bracket (taxable income of $18.3 million and for 35%) and that tax credit would
be given for years 1 and 2 during which the firm would incur losses.
Financial Projections
206
C
E
-W
MART
M1
M2
M3
hN~mhm~-m1
M4
MS
M6
TWai
M7
M8
M9
M10
M11
A12
350
350
350
350
350
35
2,100
M r
88
263
24
88
263
263
2,100
525
L575
E
License Fees and Royalties
Tech Services &Development
E
o
o
a.
Eq4unt and Supies
350
88
TaoW evane
Cost of Sales
GMsP t
263
_
Operating
88
263
__penses
Research and Development
-
-
1,258
SG&A
TaltperatgLFpn=se
Pn& beheerestamdTau
-
-
153
1,411
1,258
153
1,411
1,258
153
1,411
1,258
153
1,411
1,258
153
1,411
1,258
153
1,411
(1,149)
(207)
(1,149)
(207)
(1,149)
(1,149)
(207)
(1,149)
(207)
(1,149)
8,468
(6,893)
(207)
(1,240)
(1,356)
(1S.133)
InterestExpense
Taxes Inciured
Net
ln1come
-
-
.
-
-
-
1.35 6) 1
.L3;6
(207)
11.3-46
(1J.
3566
7,548
920
......
.......
......
..........
..
......
.. .........
Technolog es Pro Forma Income Statement - 2012
MO T
Q1
Q2
Q3
Q4
Total
1,050
1,050
1,050
1,050
4,200
Tech Services & Development
-
-
-
-
-
Equipment and Supplies
-
-
-
Total Rewnue
1,050
1,050
1,050
1,050
4,200
Cost of Sales
Gross Profit
263
788
263
788
263
788
263
788
1,050
3,150
2,762
265
3,027
2,762
265
3,027
2,762
265
3,027
2,762
265
3,027
11,048
1,060
12,108
(2,240)
(740)
(2,240)
(740)
(2,240)
(740)
(2,240)
(740)
(8,958)
-
-
License Fees and Royalties
SG&A
Research and Development
Total Operating Expenses
Profit before Interest and Taxes
Interest Expense
Taxes Incurred
-
-
(2,960)
-
hLD Technolo-gies Pro Forma Income Statement -2013
Q-1
License Fees and Royalties
Tech Services & Development
Equipment and Supplies
3,360
1,035
2,750
Total Rewnue
7,145
Cost of Sales
840
Gross Profit
Research and Development
SG&A
Total Operating Expenses
Profit before Interest and Taxes
Interest Expense
Taxes Incurred
Net Income
Q2
3,360
1,035
2,750 '
7,145
840
Q3
Q4
Total
3,360
3,360
1,035
1,035
2,750
840
840
6305
6.305
,-,0,
13,440
4,140
11,000
28,580
3,360
25220
1,048
2,830
3,878
21,341
(2,960)
7,469
10,912
2,750
7,145
r
7,145
63Aa5%
6305
,0,
262
708
970
5,335
(740)
1,867
262
708
970
5,335
(740)
1,867
5,335
(740)
1,867
262
708
970
5,335
(740)
1,867
2,72S
2.728
2 728
2.728
,-6,
208
.....
.......
.............................................
hED
Forma Income Statement - 2014
Pro
Technoloies
Q1
License Fees and Royalties
Tech Services & Development
Equipment and Supplies
Total Revenue
Cost of Sales
Gross Profit
I 01wratill1g, I-AI)CIISCI,
Research and Development
SG&A
Total Operating Expenses
Profit before Interest and Taxes
Interest Expense
Taxes Incurred
Net
Income
I
Q3
Q4
Total
6,426
1,552
4,125
1,607
6,426
1,552
4,125
12,103
1,607
25,704
6,209
16,500
48,413
6,426
A407
I1097
4198Q7
Q2
6,426
1,552
4,125
12,103
1,607
6,426
1,552
4,125 '
12,103
1,607
.1 097
1 f07
12,103
1
F
A
,
,-,0,8,
262
868
1,130
262
868
1,130
262
868
1,130
868
1,130
3,470
4,518
9,367
(740)
9,367
9,367
9,367
37,469
3,279
5,349
(740)
3,279
5,349
-
1,048
(2,960)
13,114
(740)
3,279
(740)
3,279
5,349
-5,349
I
2 1,3 9
Pro forma balance sheet
I
d L. U.
C~Ommomw
w
&Me
loin
Iamm.
rmismsue
1
1
209
M1
M2
MDBTeddai*
M4
M3
4eenaaSlaomst-201I
M7
M6
MS
M8
M9
(1356)
(1356)
Netincome
Adpstments to reconce NI to NC
Increase inreceivables
se
Deciaopm
NetafraOpeadqgAdikies
(
Pwchase of equiments
NetCFhmiestimgAdkids
(P;"
I10
(OA
MO
M11
M12
ToWn
(1,56)
(1356)
(1,356)
(1,356)
(,133)
100
(1A5)
100
(5
100
100
1o
(1
(VA)
(1X"
(I)
(P;"
(I4 A)
(VA)
(
(1X"50)
(P;"
5
(125
(1^2)
600
(7
(1m)
W,0)
--
Net bomirMgs
I
50
Fmer'equiy
15,00
NetnCmFh= ing Adisides
15,550
Netacruse insCuh
U4
15,550
(Z506)
Z506)
506)
506)
O6)
)
hLTecnooge Pro Frm C StemnQ2
Q1
Net income
Adjustments to reconcile NI to NC
Increase in receivables
21
Q3
Q4
Total
(2,980)
(11,918)
(2,980)
(2,980)
(2,980)
-
-
-
-
-
-
-
-
Depreciation expense
Net CF from Operating Activities
370
(2,610)
370
(2,610)
370
(2,610)
370
(2,610)
1,480
(10,438)
Purchase of equipments
Net CF from Inves ting Activities
(2,750)
(2,750)
(2,750)
(2,750)
(2,750)
(2,750)
(2,750)
(2,750)
(11,0)
(11,000)
-
-
-
-
-
5,375
5,375
5,375
5,375
21,500
-
-
-
-
5,375
5,375
5,375
5,375
21,500
15
15
15
15
62
Q4
Total
Founders'equity
Net borrowings
Repayment
Net CF from Financing Activities
Net Increase in Cash
htFD Technologies Pro Forma CF Statement -2013
Q3
Q2
I Q1
Net income
Adjustments to reconcile NI to NC
Increase in receivables
Depreciation expense
Net CF from Operating Activities
I
Purchase of equipments
Net CF from Investing Activities
-
2,728
2,728
2,728
2,728
10,912
390
3,118
390
3,118
390
3,118
390
3,118
1,560
12,472
-
--
(250)
(250)
(250)
(250)
~
--
(250)
(25))
(1,0UU)
(250)
(250)
(1,000)
Founders'equity
-
-
Net borrowings
-
-
Repayment
-
-
-
-
-
-
-
2,868
2,868
2,868
2,868
11,472
578
3,446
6,314
9,182
578
Net CF from Financing Activities
Net Increase in Cash
211
...
I
.......
I....
.. .. ....
.............
..
-'
---- .
-
- --
hLED Technologies Pro Forma CF Statement -2014
Q3
Q2
1 Q1
Q4
Total
("IS11 HoN From Ojx ratillg ActiNities
Net incone
Adjustments to reconcile NI to NC
Increase in receivables
Depreciation expense
Net CF from Operating Activities
I
5,349
5,349
5,349
5,349
'21,395
410
5,759
410
5,759
410
5,759
410
5,759
1,640
23,035
- - --
(250)
(250)
Purchase of equipnrnts
Net CF from Invsting Activities
Founders'equity
(250)
(250)
(250)
(250)
(250)
(250)
(1,000)
(1,000)
-
-
-
-
-
-
-
5,509
5,509
5,509
5,509
22,035
12,050
17,559
23,067
28,576
12,050
Net borrowings
Repaynent
Net CF from inancing Activities
Net Increase in Cash
Breakeven Analysis
Breakeven Analysis
90,000
80,000
70,000
60,000
4-
50,000
-Ar-Revenue
40,000
--
TotalCost
30,000
20,000
10,000
2011
2012
2013
2014
2015
The breakeven analysis shows that hLED Technologies will reach its breakeven point in
2013, the third year of its operations after the 2 years of significant initial R&D phase.
Based on initial customer response and market surveys, hLED Technologies feels
confident that demand and pricing power is strong. Therefore, it is anticipated that
212
......................
internal cash flow could be stronger than projected. Since a large percentage of the
revenue is based on license fees and royalties, hLED could discuss upfront fees with
customers to reach breakeven more quickly. Additionally, hLED does not anticipate
needing funding after year 3. Although the initial development costs are high, future
cash flow margins are high enough to support necessary expansion. The size of the gross
margins is illustrated below:
Gross Margin
2011
2012
75%
75%
2013
88%
2014
2015
87%
84%
As shown, the size of gross margins is big and price sensitivity is minimal given that
licensing fees tend not to vary a lot. We also assumed a conservative rate of 5%, our
sales projections were also conservative relative to the advantage of the technology and
our potential market share, and we made conservative assumptions about technology
services and equipments. Should the venture fall short of sales projections, the
breakeven point will shift slightly more to the right, but we assumed fees and purchases
from a small number of clients, so it should not shift more than a year unless there is a
dramatic change in the landscape of the display market.
Financial Oversight and Cost Control
Because of the capital-intensive nature of hLED, costs are a very important part of the
project. As a startup, it's entirely on us to keep our costs low. Initially, we considered
hiring an outside auditor, but realized that would be expensive and unnecessary
because our own interests are aligned with those of the company.
We plan on self-policing by having each group at the company report their costs
monthly to an individual on the team. This auditor will be changed to a different team
member each month. This will have two effects: 1) it will force each individual on the
team to have an in-depth understanding of our costs, and 2) it will require the auditor to
transfer his knowledge to the next auditor, which will facilitate further knowledge
transfer throughout the organization.
We have a small team, so if there are significant budget overruns, we will meet up and
discuss how to alleviate the budget problems. Budget problems will mean further
oversight by the rest of the team to ensure the offender doesn't exceed their budget.
In terms of funding, hLED will seek approximately $20 million in government grant and
loans. We believe government funding to be appropriate for the initial stages of cash
shortfall when developing our product with the avionics market. In addition, we will be
able to maintain tight control over the ownership structure by avoiding shareholder
equity dilution. We do not anticipate the need for additional rounds of funding as the
cash flow margins are projected to be high enough in subsequent years as we target the
consumer display market with fully-developed capabilities.
213
Exit Strategies
In terms of exit strategies, hLED Technologies could sell the business or the license
portfolio to an existing licensing company, manufacturer or buyout firm. Alternatively,
the firm could also grow the business around hLED licenses and then liquidate the firm
once the opportunities have been depleted. We will continue to monitor exit
opportunities throughout the life of the firm.
Ownership
The table below provides founders' allotment:
Founder
Nathan Trujillo
Eric Lam
Hai Liu
Kiran Divvela
Yoomi Hong
Total Ownership Allotment
27%
25%
16%
16%
16%
Vesting Schedule (one year cliff)
4 years
4 years
4 years
4 years
4 years
We have instituted a four-year vesting schedule that rewards time with the company.
The vesting schedule has a one-year cliff, after which founders will receive 1/16 of their
equity each quarter for four years. In recognition of the contribution of the founders'
effort to this point, everyone will receive 1%of equity upfront. Nathan, who has
previously spent significant time and effort on this project, will receive an additional 6%
of his equity upfront.
hLED Technologies will initially issue 1,500,000 shares. We will set aside 500,000 shares,
which would be held by an employee options pool. 7%of Nathan's equity and 1%of
everyone else's equity will vest immediately, so the initial share split would be:
Founder
Nathan Trujillo
Eric Lam
Hai Liu
Kiran Divvela
Yoomi Hong
Total
Shares Vested
18,900
2,500
1,600
1,600
1,600
26,200
After 1 year of operation, if all five founders are still actively involved in the business, X
of the remaining founders' equity will vest.
Founder
Nathan Trujillo
Eric Lam
Hai Liu
Kiran Divvela
Yoomi Hong
Total
Additional Shares Vested
65,732
60,863
38,952
38,952
38,952
243,450
214
. ......
...........
........
. ..
The result of this distribution schedule will be that, if at the end of four years all five
founders are still actively involved with the company, they will own the following
number of shares:
Shares Vested
270,000
250,000
160,000
160,000
160,000
1,000,000
Founder
Nathan Trujillo
Eric Lam
Hai Liu
Kiran Divvela
Yo omi Hong
Total
Beyond founder's equity, we anticipate allocating some equity to future key hires. For
example, additional management will be considered based on the progress of the
company. There would be 500,000 additional shares held in the employee options pool
and we expect that some of the founders will leave the company before the four-year
vesting period, thus freeing up additional shares to be sold.
We plan to maintain tight control over our equity and fund the cash shortfalls that will
occur in the development stage almost entirely through government funding, as
mentioned above.
Share Vesting Schedule
Term
Immediate
Q1
1,600
1,600
1,600
1,600
26,200
26,200
9,738
11,338
60,863
87,063
ric Lam
Cumntv
Hai Liu
Cuitv
18,900
18,900
2,500
2,500
1,600
1,600
35,333
Cumltv
Shares
Vested
Cumltv
Cumltv
Kiran
Divvela
16,433
Vesting
this
Period
Yoomi
Hong
Nathan
Trujillo
Cumltv
15,216
17,716
9,738
11,338
9,738
11,338
9,738
21,076
9,738
21,076
9,738
21,076
60,863
147,925
2
16,433
51,766
15,216
32,931
Q3
16,433
68,199
15,216
48,147
9,738
30,814
9,738
30,814
9,738
30,814
60,863
208,788
Q4
16,433
84,632
15,216
63,363
9,738
40,552
9,738
40,552
9,738
40,552
60,863
269,650
60,863
330,513
Q5
16,433
101,064
15,216
78,578
9,738
50,290
9,738
50,290
9,738
50,290
Q6
16,433
117,497
15,216
93,794
9,738
60,028
9,738
60,028
9,738
60,028
60,863
391,375
Q7
16,433
133,930
15,216
109,009
9,738
69,766
9,738
69,766
9,738
69,766
60,863
452,238
Q8
16,433
150,363
15,216
124,225
9,738
79,504
9,738
79,504
9,738
79,504
60,863
513,100
573,963
Q9
16,433
166,796
15,216
139,441
9,738
89,242
9,738
89,242
9,738
89,242
60,863
Q10
Q11
16,433
183,229
15,216
154,656
9,738
98,980
9,738
98,980
9,738
98,980
60,863
634,825
16,433
199,662
15,216
169,872
9,738
108,718
9,738
108,718
9,738
108,718
60,863
695,688
Q12
16,433
216,095
15,216
185,088
9,738
118,456
9,738
118,456
9,738
118,456
60,863
756,550
Q13
16,433
232,527
15,216
200,303
9,738
128,194
9,738
128,194
9,738
128,194
60,863
817,413
14
16,433
248,960
15,216
215,519
9,738
137,932
9,738
137,932
9,738
137,932
60,863
878,275
Q15
16,433
265,393
15,216
230,734
9,738
147,670
9,738
147,670
9,738
147,670
60,863
939,138
Q16
16,433
281,826
15,216
245,950
9,738
157,408
9,738
157,408
9,738
157,408
60,863
1,000,000
215
........
......
.....
..............
Financial Conclusions
In spite of the high initial development costs, capital expenditures and administrative
expenses are expected to be low due to the inherent cost advantage that the
technology has and the expected funding for military applications.
The main source of revenue for hLED will be IP licensing fees and royalties, but
additional revenue can be generated from co-developing and supporting a supply chain
that has the capability to supply the global display and lighting markets with the
materials and services needed to manufacture hybrid LED devices through the use of
strategic partnerships.
As a result, the firm is projected to reach breakeven by year 3 and achieve net profit of
$40 million by year 5.
We will seek to receive $20 million in government funding. We expect the firm's
financing needs to be minimal thereafter. Given the strong expected cash flow, we do
not plan on obtaining additional funding during this phase.
There are several viable exit strategies for hLED including sale or liquidation of the
business and we will continue to monitor various opportunities as the firm matures.
Addendum: Cap Chart
%Share CapAnit
Founders
1,000,000 100.0%
66.7%
1,000,000
0.1%
66.7%
$50
Shares
1,000,000 100.0%
66.7%
$0
0
0.0%
0.0%
$40,000
0
99.9%
0.0%
$0
0
0.0%
0.0%
ESOP
0
500,000
0.0%
33.3%
0
500,000
0.0%
33.3%
0
500,000
0.0%
33.3%
Total
$50
100.0%
$50
1,500,000 100.0%
100.0%
Govt Grant+Loan
1,500,000 100.0%
100.0% $40,050
1,500,000 100.0%
Valuation Multiples % Changes in the Value of Ownership Stakes
Changes in Valuation Mfultiples & Value of Ownership Stakes
2011
Valuation Multiple
0.00x
2012
2013
2014
2015
0.00x
0.12x
0.84x
1.07x
Nominal Value
0
0
1,257
17,047
40,931
Value of Ownership Stakes
0
0
1,257
17,047
40,931
216