Molecular Resists for EUV Lithography:
A Progress Report
Professor Clifford L. Henderson
School of Chemical & Biomolecular Engineering
Georgia Institute of Technology
Atlanta, GA USA
School of Chemical & Biomolecular Engineering
Georgia Tech
Chemically Amplified Resists (CARs)
1.
2.
Photoacid Generator
(PAG)
− (CH2 − CH)n −
insoluble
polymer
O
hυ
H+
H2 O
Acid (H+ )
− (CH2 − CH)n − +
OH
O
O
+ H+
soluble
polymer
OHaqueous base
Expose
Heat
School of Chemical & Biomolecular Engineering
Base
Georgia Tech
2
Inherent Problems with CARs
Image Blur
Line Edge Roughness (LER)
Traditional CAR 3σLER: > 10nm
Traditional CAR photoacid diffusivity: > 10nm
> 150 nm
100 nm
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3
Challenges for Future Resists
•
•
We are currently working on next
generation 193 nm, EUVL, and ebeam resists
In particular, 2005 ITRS Roadmap
lists the following three criteria as
major challenges for EUV resists
– obtaining < 3 nm 3σ LWR
– obtaining < 10 mJ/cm2 sensitivity
– obtaining < 40 nm ½ pitch
resolution
Important factors controlling all three
behaviors appear to include:
– Photoacid diffusion
– PAG loading
– Inhomogeneous distribution of
resist components such as PAG
– Size of resin molecules
– Compositional control of resin
molecules
LER
Sensitivity
0.8
0.6
0.4
200 nm
3 mol%
5 mol%
10 mol%
15 mol%
0.2
0
0
School of Chemical & Biomolecular Engineering
Resolution
1
Normalized Film Thickness
•
4
2
4
6
2
Dose (mJ/cm )
8
10
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5
The RLS Tradeoff
LER
LER
Resolution
Sensitivity
Resolution
Sensitivity
Resolution3 × LER 2 × Sensitivity ≈ constant
•
•
•
There exists a well known trade-off in resolution, LER, and
sensitivity for chemically amplified resist materials
Although the RLS limitation is intrinsic to CARs, if the constant term
is made small enough, then they can obtain the desired
performance metrics.
Modern blended PAG CAR designs appear to have minimized the
constant term near its limits, but performance still does not meet the
requirements.
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6
Possible Solutions #1: Base Quenchers
Base
Quencher
Photoacid
Neutralized
Photoacid
Critical Problems:
1. Acid/base molecules exhibit nonuniform distribution.
2. Photosensitivity significantly
reduced as base concentration is
increased.
Base quencher molecules are added to limit the diffusion
range of photoacid and improve environmental stability.
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Possible Solution #2: Low Ea Resists
G. M. Wallraff, et. al., JVSTB 2004
Problems:
1. Studies have shown low activation energy materials exhibit
more substantial outgassing.
2. Have still generally shown poor LER/LWR performance.
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7
8
Possible Solution #3: Molecular Glass Resists
Polyhydroxystyrene
(50 repeat units)
TPS.Nonaflate
Resist monomer
5~10 nm
Da Yang, et. al., J. Materials Chemistry 2006
Advantages:
1. Reported low LER (3σ LER ~5 nm).
2. Better phase compatibility with PAGs.
Potential Problems:
1. Does not directly address acid diffusion
and may in fact make it worse.
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9
Molecular Resists
•
Despite the reduction in pixel size – LER still 5-9 nm on average –
long range LER not effected by pixel size thus far
• Resolution still limited by photoacid diffusion blur
• Blended systems – resist/PAG/base – lead to inhomogenity and LER
• Multiple reactive sites on a molecule lead to distribution of protecting
- still not monodisperse = inhomogenity
Effect of PAG homogeneity
Hirayama, et al. Jap. J. App.
Phys. 44, 5484, (2005)
Increasing homogeneity
Decreasing LER
Effect of
distribution of
protecting groups
Shiono, et al. SPIE 6519,
65193U, (2007)
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10
Possible Solution #4: Polymer-bound PAG Resists
Example cation-bound PAG resist
+
C O
O
+
y
z
C O
O
C O
O
x
C O
O
Polymerization
AIBN, THF, 65oC, 24h
OH
OH
S+
S+
Current Ongoing UNC-Charlotte –
Georgia Tech – Intel Program
C4F9
O
S OO
C4F9
O
S OO
Example anion-bound PAG resist
+
C O
O
C O
O
x
THF / CH3CN
+
SO3-
OH
AIBN, 65oC, 24h
y
z
C O
O
C O
O
OH
SO3-
+
S
3
+
S
Advantages:
3
1. Substantially higher PAG loadings are possible (retain sensitivity
with reduced acid diffusion).
2. Eliminates segregation and inhomogenous PAG distribution.
3. Permits direct acid diffusion control.
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LER Comparison for EUV blended & bound CARs
y
z
C O
O
C O
O
F
F
x
C O
O
OH
Blend
C O
O
F
F
F
F
OH
F
F
y
x
SO3-
SO3+
S
+
S
3
3
HOST-EAMA-F4-MBS.TPS
Mole Feed Ratio
Polymer
HOST
EAMA
HOST-EAMA blend
F4-IBBS.TPS
40
60
HOST-EAMA-F4MBS.TPS
25
72.5
HOST-EAMA Blend F4-IBBS.TPS
Polymer Composition
PAG
2.5
School of Chemical & Biomolecular Engineering
Yield / %
Mw
(PDI)
Stability /
oC
Tg
/ oC
HOST
EAMA
PAG
45.8
54.2
7.1
(wt%)
58.5
4500
(2.5)
156.9
113.2
35.0
57.9
7.1
37.3
3600
(1.6)
138.1
**
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11
Spatial-frequency dependent LER for
EUV blend and polymer-bound PAG samples
HE-F4-MBS.TPS
(124 uC/cm2)
HE + F4-IBBS.TPS
(120 uC/cm2)
Sigma vs L
L
We believe this improvement is
due to:
- homogenous PAG distribution
- higher PAG loading
- reduced photoacid diffusion
School of Chemical & Biomolecular Engineering
„ Polymer-bound PAG sample showed 50%
smaller 1σ LER (1.05 nm) than the blend
one (1.60 nm). This result corresponds to
1.65 nm difference in the 3σ LER .
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12
13
Lessons Learned So Far
• Polymer-bound PAG Resists
– Binding anion to polymer reduces photoacid diffusivity substantially
while binding cation has little effect
– Bound-anion materials show significantly better LER performance
than analogous blended or cation-bound resists
– High PAG loading possible in these systems maintains photospeed
CONCEPT:
Combine
the best of both solutions
comparable to
blended systems
High PAG loadings
appear
to lead to lowermolecular
possible LER glass
by– making
single
component
•resists
Molecular
Glass
ResistsPAG functionality directly in
that
contain
Smaller molecular size does appear to have some advantage for
the– molecule.
improving ultimate LER performance
– Exact control over molecular structure eliminates problems with
inconsistency in terpolymer polymerization
– Superior dissolution properties – each molecule in the glass is
identical, while in the polymer there is a distribution of molecular
weights and chain lengths; polymer chains can be partiallydeprotected
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Positive Tone Materials
School of Chemical & Biomolecular Engineering
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Possible Solution #5: Single Component
Molecular Resists
Protecting Groups
Sulfonic Acid
O
O S
O
Photoacid Generator
Molecular Glass Core
• Single molecule resist = molecular resist that contains PAG
functionality and acid labile protecting groups on a base soluble, etch
resistant molecular glass core.
• Provides three distinct advantages over current CAR materials
1. complete homogeneity
2. very high PAG loading
3. high level of diffusion control
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15
16
Homogeneity: A Key Enabler
• Single component resists provide the ultimate in
homogeneity because of their small molecule, single
component nature.
• No physically blended additives = no phase separation
or aggregation of components
• Small molecules = full synthetic control of
stereochemistry and regiochemistry and can allow for
completely monodisperse resists.
• Even in the event of reactions at multiple functional sites,
standard chromatographic separation should allow for
excellent separation of isomers.
• This provides advantages over polymer-bound PAGs
which are typically composed of complex ter- and
tetrapolymers which would display larger polydispersity
and variations in chain compositional uniformity.
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17
Use of High PAG Loadings
•
•
Very high PAG loading provides a number of advantages.
High PAG loading should improve sensitivity.
– Since standard resists contain only around 5 percent PAG, the film quantum
yield (moles of acid produced per mole of photons incident on the film) is
reduced because much of the incident energy does not reach a PAG and is
wasted.
•
Simulation and experimental results have shown that increased PAG
loading and quantum yield improves not just sensitivity, but also
simultaneously improves LER [Van Steenwinckel Proc. SPIE 2007, 6519,
65190V and Choi, K.; et. al. Proc. SPIE 2007, 6519, 651943]
– This is because the higher photoacid concentration in the exposed resist has
less statistical spatial variation compared to lower acid concentrations. [Lawson
Proc. SPIE 2008 Paper 6923-27]
•
•
Simulations also suggest that in the regime of high PAG density &
increased quantum yield should only slightly reduce resist resolution.
[Gallatin, Proc. SPIE, 2007, 6519, 651911]
These results suggest that increased PAG loading provides perhaps the
most promising way to improve the RLS tradeoff
= PAG
= Resist
School of Chemical & Biomolecular Engineering
Increased
PAG loading
5%
35%
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18
Acid Diffusion Control
•
•
•
•
•
Acid diffusion produces a number of effects in the CAR.
A very significant effects of diffusion is blurring of the feature.
A favorable way of reducing the acid diffusion coefficient is to increase the
size of the acid anion; it is the more favorable approach because it allows
optimal PEB temperatures for the deprotection reaction.
This approach has been used in polymer-bound PAGs to obtain sub-30 nm
resolution; the single molecule analogue to this would be to covalently bind
the PAG acid anion directly to a large molecular glass core (as depicted in
Figure 1) to create a molecular glass bound PAG.
It is an improvement over the polymer-bound PAG for two main reasons:
– (1) the polydispersity of polymer-bound PAG resists directly leads to a
distribution of acid diffusion coefficients throughout the resist, a single molecule
resist is monodisperse, so it should have uniform acid diffusion throughout the
resist
– (2) the diffusion coefficient could in principal be fine-tuned by using molecular
glass cores of larger and smaller size and volume to find the optimal diffusion
coefficient for a given patterning task
O
HO S
O
O
HO S
O
O
HO S
O
Decreasing Diffusion Coefficient
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19
Mesoscale Resist Simulations
•
Model is composed of a 2D grid
with 1 nm X 1 nm size.
O
O
O
XO
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
S+
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Model assumes constant Dill C =
0.03 = 95% of all acid generated at
100 mJ/cm2
•
Generated acids random walk n
times determined by diff. coeff.
O
O
O
O
O
O
•
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Photoacid generation is controlled
by Dill C kinetics
PAcid ( x, y) = PPAG ( x, y)[1 − exp(−C ⋅ dose( x, y))]
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
•
O
O
O
O
O
O
O
O
O
O
O
O
O
•
The grid contains resist molecules
and PAGs which all have the same
number of protecting groups.
O
O
O
O
X
O
O
O
O
O
O
O
S+
TAS-tBoc
O
O
THPE-tBoc
O
School of Chemical & Biomolecular Engineering
O
O
O
O
n=
τ
t Bake
2d 1
=D 2
a t Bake
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20
Additional Model Details
•
•
•
•
Perfect aerial images have been used to study pure material responses
Model generates individual photoacids and allows them to random walk
around carrying out deprotection.
When the photoacid lands on a grid point, it carries out a single deprotection
reaction.
Deprotection is converted to imaged feature by threshold removal of
molecules.
Acid Distribution
Deprotection Extent
140
0
120
0
100
0
Resolved Image
1
0.9
0.8
0.7
140
120
100
y (nm)
0.6
80
0
60
0
40
0
0.5
0.4
0.3
80
60
40
0.2
20
0
20
40
60
80
x (nm)
100
120
140
0.1
20
School of Chemical & Biomolecular Engineering
40
60
80
x (nm)
100
120
140
0
20
20
40
60
80
x (nm)
100
120
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140
21
Effect of Photoacid D & Acid Content
11
56
10
54
53
52
51
Diff. Coeff.
(nm2/s)
50
49
0.07
0.09
0.15
48
47
•
•
•
20
40
60
80
2
Dose (mJ/cm )
100
Increasing D
9
Diff. Coeff.
(nm2/s)
0.07
0.09
0.15
8
7
6
5
46
0
3σ LER (nm)
Critical Dimension (nm)
55
120
Increasing D
4
0
20
40
60
80
2
Dose (mJ/cm )
100
120
At low dose (less acid), increasing diffusion coefficient decreases
LER, while at higher dose (more acid), increasing diffusion
coefficient increases LER.
Lower acid conc., the acids are spaced farther apart physically and
thus the larger diffusion coefficient acts to smooth out the
inhomogeneity.
Higher acid loadings, the acids are closer together and more evenly
distributed, the higher number of acids increase the probability of
random diffusion outside the line edge.
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22
Effect of Photoacid D & Acid Content
Acid Distribution
Low D
High D
Line Edge
Low Dose
High Dose
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23
Effect of PAG Loading
25
Increased PAG
PAG Loading
0.05
0.1
0.25
0.5
1
3σ LER (nm)
20
15
10
5
constant LER
0
0
20
constant dose-to-size
•
40
60
80
2
Dose-to-Size (mJ/cm )
100
120
High PAG loading allows improvement in LER and sensitivity
compared to current loadings – with no penalty in resolution
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LER vs. Acid Concentration
3σ LER at E Size (nm)
25
PAG Loading
0.05
20
0.1
0.25
15
0.5
10
5
1
1
LER = 278
# Acids
Increasing PAG
0
100
•
1000
Number of Acids at ESize
10000
Using photoacid concentration instead of dose collapses onto a
single curve
LER ∝ 1 [ Acid ]
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24
Coupling of Number of Protecting Groups &
Acid Diffusion Coefficient
nonamplified
behavior
•
More protecting groups allow same imaging LER with larger
diffusion coefficient, or lower LER at a given photoacid D
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25
26
RLS for High PAG Loading Materials
LER
LER
increased PAG loading
Resolution
Sensitivity
Resolution
Sensitivity
•
Increased PAG loading provides way to break through current RLS
limitations
•
LER is controlled primarily by acid concentration at sizing dose –
higher acid concentration = lower LER
•
Higher PAG loadings require lower diffusion coefficients for both CD
control and achievement of minimal LER
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From Blended Star Shaped Molecular
Resists to Single Component Molecular
Resists Contain PAG Functionality
O
O
O
O
O
O
HO
Cl
-
OH
S+
O
O
OH
O
O
O
SbF6
O
O
S
HO
O
-
Cl
-
OH
O
S+
+
O
O
OH
O
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27
Synthesis of Triarylsulfonium (TAS)
Molecular Resist
CH3
Synthesis
3
AlCl 3
O
OH
S
Cl
Cl
0-20
-
Cl
HO
OH
S+
oC
CH3
OH
O
Cl
HO
Protection
-
OH
O
O
S+
O
O
O
O
DMAP
O
O
Cl
-
O
O
S+
MeCN
24 hrs
OH
O
O
O
O
Metathesis
O
O
O
Cl
-
O
O
O
O
S+
SbF6
O
-
O
O
O
S+
NaSbF6
EtOH/H2O
O
O
O
School of Chemical & Biomolecular Engineering
O
O
O
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28
29
TAS-SbF6 NMR
O
O
-
O
SbF6
O
O
O
S+
C
B
O
A
H2O
B
A
O
27.0
DMSO
O
18.0
6.0
C
10.0
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
School of Chemical & Biomolecular Engineering
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
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30
TAS-tBoc-SbF6 E-beam Litho
75°C PEB
80 nm 1:1
200 nm
•
•
TAS-tBoc-SbF6
50 nm lines
200 nm
60°C PEB
70 nm 1:1
200 nm
60 nm 1:1
200 nm
50 nm 1:1
200 nm
Dose = 512 μC/cm2
Dose = 1000 μC/cm2
LER (3σ) = 3.9 nm
LER (3σ) = 9.9 nm
PEB of 75°C allowed patterning
down to 80 nm nominal 1:1
line/spacing – smaller lines limited
by pattern collapse (2.5:1 aspect
ratio)
Photoacid diffusion blur is still a
problem; 80 nm nominal actually
resolved 50 nm lines, 110 nm
spaces
School of Chemical & Biomolecular Engineering
•
•
•
PEB of 60°C allowed patterning
down to 50 nm nominal 1:1
line/spacing
Photoacid blur reduced, but LER
and dose higher
Behavior is likely due to some
combination of diffusion &
deprotection kinetics limitations
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31
TAS-tBoc-SbF6 EUV Results
60 mJ/cm2
30 nm 1:1
50 nm 1:1
•
•
•
•
•
Passed outgassing tests at U.Wisconsin
– bulky ring subs. Improves outgassing
EUV exposures done on PSI tool in
Switzerland courtesy of Intel
50 nm 1:1 lines resolved with low LER of
5.2 nm
30 nm 1:1 lines do not appear to open,
even at high dose
Failure not due to acid blur, but due to
diffusion/kinetic limitations
School of Chemical & Biomolecular Engineering
200 nm
LER (3σ) = 5.2 nm
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32
TAS-tBoc-X Family
O
O
O
X
O
O
Cl
TAS-tBoc-Cl
O
S+
SbF6
X
=
TAS-tBoc-SbF6
O
O
O
O
•
•
•
•
•
O S CF3
O
TAS-tBoc-Tf
O
O S (CF2 )3 CF3
O
TAS-tBoc-Nf
O
O S
O
TAS-tBoc-Ts
Five different TAS derivatives synthesized to examine effect of acid
size and acid strength
TAS-tBoc-Cl soluble in water
TAS-tBoc-Ts soluble in water, but shows excellent negative tone
behavior in pure water development (SPIE 2008 Paper 6923-57)
TAS-tBoc-Nf will not form films – adhesion problem
TAS-tBoc-SbF6 and TAS-tBoc-Tf studied as high resolution positivetone platforms
School of Chemical & Biomolecular Engineering
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Single Component Acid Bound Resists
(SCABRes)
Protecting Groups
Sulfonic Acid
O
O S
O
O S
O
O
O
33
F
O
F
O
O
F
O
O
O
O
O S
F
O
Photoacid Generator
N
O
CF3
N
O
O
N
O
Molecular Glass Core
HO
OH
OH
O
OH
S
OH
HO
O
O
HO S
O
HO
OH
OH
•
•
•
•
•
•
OH
Originally proposed at SPIE 2007 as evolution of TAS materials
Design covalently binds sulfonic acid moiety directly to larger molecular glass
core to control photoacid diffusion - improving both resolution and LER
Resist design space greatly increased compared to TAS allowing for
systematic variation of each component
Multi-functional cores allow selective attachment of acid and PAG, maintaining
high homogeneity in a complex molecule
Acid can be selectively attached to core or designed directly on the core
Non-ionic PAGs now available to improve solubility issues with TAS
School of Chemical & Biomolecular Engineering
OH
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34
NBB : NDI-BHMOBS-Boc
Molecular Glass Core
Sulfonic Acid
Protecting Group
O
O S
O
Photoacid
Generator
•
•
•
•
•
•
O
HO
NBB first example of non-ionic bound sulfonic acid molecule resist
Sulfonic acid is directly part of molecular glass core
Norbornene dicarboximide PAG
Superior solubility in casting solvent as compared to TAS compounds
Has good adhesion and forms excellent films
Zero dark loss over 30 sec. development in 0.261N TMAH
1. pyr, THF
O
S OH 2. hexane
O
OCH3
90%
O
HO
+
O
S O
O
OCH 3
HN
SOCl 2
O
HO
70%
School of Chemical & Biomolecular Engineering
NDI-OH
O
S Cl
O
OCH3
pyr, THF
45%
O
HO
O
O
S O N
O
OCH3
Boc2O
DMAP, CH2Cl 2
O
O
O
O
O
54%
O
O
S O N
O
OCH3
Georgia Tech
O
NDI-BHMOBS-tBoc E-beam Litho
•
90oC PEB
•
γ = 5.8
•
•
•
100 nm 1:1
90 nm 1:1
80 nm 1:1
School of Chemical & Biomolecular Engineering
35
NDI-BHMOBS-tBoc shows reduced
sensitivity under 100 keV e-beam
compared to TAS ~ 3x of TAS
Excellent image quality and resolution,
down to at least 40 nm 1:3 lines/space
No appreciable acid blur, even at 90oC
PEB, above Tg
Excellent LER (3σ) = 4.6 nm
Suffers from pattern collapse starting at 60
nm 1:1 lines (aspect ratio > 2) using current
developer and rinse protocols
70 nm 1:1
60 nm 1:2
50 nm 1:3
40 nm 1:3
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36
36
EUV Exposures of NBB
50 nm 452
•
•
•
•
•
50 nm 497mJ/cm2
30 nm 452
25 nm 452
452 mJ/cm2 correct dose-to-size for 50 nm lines – 497 mJ/cm2
shows over-dose (larger spaces) – both have undesirable LER
30 nm and 25 nm lines do not appear to open at 452 mJ/cm2
Possible cross-linking mechanism provided by benzophenone
moiety
Glass core is still not desired size
PAG “chromophore” has not been optimized
School of Chemical & Biomolecular Engineering
Georgia Tech
Negative Tone Materials
School of Chemical & Biomolecular Engineering
Georgia Tech
Our Early Work – EIPBN 2007
O
O
O
O
O
O
•
•
•
•
•
•
3-Ep has excellent LER and resolution
Excellent sensitivity
50 nm 1:1 line/spacing - aspect ratio ~ 3:1
30 nm 1:3 line/spacing - aspect ratio ~ 4:1
Pattern collapse for smaller lines
LER (3σ) = 2.3 nm
EIPBN 2007, JVSTB Nov/Dec 2007
School of Chemical & Biomolecular Engineering
Georgia Tech
38
39
Synthesis of First Generation Ep
Molecular Resists
O
O
O
HO
O
OH
H
O
OH
Cl
H+
2
O
MeOH/H2 O
3-Ep
K2 CO3, 18-C-6
Me2 CO
OH
O
OH
O
O
HO
O
OH
H
4
H
O
OH
O
O
O
O
Cl
H+
MeOH/H2 O
4-Ep
K2 CO3, 18-C-6
Me2 CO
HO
OH
O
O
O
O
• Simple two-step synthesis
– Make polyphenol core
– Functionalize phenol sites to make epoxy functional groups
School of Chemical & Biomolecular Engineering
Georgia Tech
40
4-Ep 100 keV E-beam Imaging
100 nm 1:1
70 nm 1:1
30 nm 1:1
• Imaging doses in the range of 20-30 μC/cm2
• LER 3σ (4-Ep) = 2.3 nm
• Aspect ratios of at least 2.5:1 easily achieved
• Acid and/or monomer mobility appears to becomes important below
30 nm feature sizes
School of Chemical & Biomolecular Engineering
Georgia Tech
41
EUV Exposures of 4-Ep
50 nm
•
•
•
32 nm
4-Ep resist is very sensitive, dose to size in the range of 18-24 mJ/cm2
LER is good compared to other materials exposed on PSI tool but still
significantly worse than for 100 keV e-beam exposures
Resist formulation and development protocols are still relatively unoptimized
School of Chemical & Biomolecular Engineering
Georgia Tech
42
Next Generation Ep Molecular Resists
PAG
PAG
O
Extending the Ep Resist Design
• Explore polymerization routes and initiators that
can use lower processing temperatures
• Further explore functionality dependence
PG
• Tether acid counter-ion directly to molecular
glass
O
O
S
O
Molecular
Glass Core
O
O
PG
School of Chemical & Biomolecular Engineering
Georgia Tech
PG
Conclusions
• High PAG loading materials are promising
– Covalent inclusion of PAG into resist molecule allows full range of
molar loadings
– LER ∝ 1 [ Acid ]
• Heterogeneity in resist film is BAD for LER
– Single molecule materials ensure homogeneity at molecular scale
• Acid diffusion and number of protecting groups must be
tuned properly to achieve lowest LER
• Both positive and negative tone molecular resists are
promising
School of Chemical & Biomolecular Engineering
Georgia Tech
Summary
44
• Significant materials challenges lay ahead for lithography
• Obtaining needed LWR and resolution will likely require
new resist designs beyond conventional blended CARs.
• Molecular glass resists may offer ultimate performance.
• High PAG loadings are a key method for extension of
CAR like designs to low LER, high resolution imaging
• We have designed, synthesized, and characterized first
examples of positive tone single component molecular
glass resists.
• Ionic and non-ionic systems have been demonstrated.
• Negative tone blended Ep molecular resist systems have
shown great promise as both e-beam and EUVL resists.
• Systematic studies of structure-property relationships in
these various material families are underway.
• Novel methods for better utilization of beam energy being
explored.
School of Chemical & Biomolecular Engineering
Georgia Tech
45
Acknowledgements
• Cody Berger (ChBE), Cheng-Tsung Lee (ChBE),
Richard Lawson (ChBE), Robert Whetsell (Chem)
• Georgia Tech Microelectronics Research Center
(MiRC) and Nanotechnology Research Center (NRC)
• Prof. Laren Tolbert (GT Chem. & Biochem.)
• Prof. Kenneth Gonsalves & his group (UNCC)
• Wang Yueh, Jeanette Roberts, Todd Younkin, Steve
Putna (Intel)
• Intel
• AZ Electronic Materials
• PSI
School of Chemical & Biomolecular Engineering
Georgia Tech
46
Questions??
School of Chemical & Biomolecular Engineering
Georgia Tech