Advanced
Manufacturing
Choices
ENGR 165- 265
Spring 2014, Dr. Lawrence Kulinsky
Scanning Proximal Probe
Lithography
• Electrical field of a Scanning Proximal Probe to
modify substrate region directly under the tip
• Mechanical methods where Atomic Force
Microscope (AFM) tip directly affects the
substrate via scraping, thermal deformation or
material transfer (such as dip-pen lithography
(DPL))
• Near-Field Scanning Optical Microscopy
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Photolithography in Distress
• From Rayleigh equation with,  = 193nm, NA = 0.93
and k1 = 0.25 or
• There are technical challenges and financial
constraints facing F2 157 nm system
• E-beam and ion beam lithography can be used to
achieve better resolution, but even these system
suffer from deficiencies such as proximal effects
Scanning Tunneling Microscope
• Invented in 1981 by Gerd Binnig and Heinrich Rohrer
(at IBM Zurich) – Nobel Prize in Physics (1986)
• Small (< 1 m) probe is scanned over sample’s
surface with typical separation of 3 to 10 Angstroms
• Piezoelectric control of the tip’s z position
• Close proximity of the tip and the surface atoms
allows for electron tunneling across the gap between
the tip and the surface
• Tunneling current is very sensitive to changes in the
gap distance – the current falls by factor of 10 with
the gap increase of 1 Angstrom
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Tunneling Quantum Effect
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Scanning Tunneling Microscope
• Small bias is
used
– 10 mV to 2 V
• Two modes
of operation:
– Constant
current
– Constant
height
http://en.wikipedia.org/wiki/Scanning_tunneling_microscope
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Scanning Tunneling Microscope
http://meso.phys.northwestern.edu/research
/low-temperature-scanning-probemicroscopy
• Resolution of STM is
determined by the
sharpness of the tip
• Tungsten tips are etched
electrochemically
• Practical STMs’ lateral
resolution – 2 Angstroms
• This resolution is more
than 1000 times better
than the diffraction
limit of optical systems
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Scanning Tunneling Microscope
Scanning Tunneling Microscopy image of graphite,
acquired under ambient conditions. Measured at the
Dept. for Earth and Environmental Sciences, LMU and
Center for NanoScience (CeNS), Munich
STM images of Si
http://www.specs.de/cms
(111)
plane.
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Atomic Force Microscope
• Major extension of STM – Atomic Force Microscope
(AFM), also known as Scanning Force Microscope
(SFM) can be used on conducting or insulating
surfaces
• Invented in 1986 by Gerd Binnig, Christoph Gerber,
and Calvin F. Quate
• The first commercial AFM was build in 1989
• Measures the force between a sharp (Si or Si3N4)
probe and the sample
SEM picture of the AFM
cantilever about 30 m wide.
http://en.wikipedia.org/wiki/Ato
mic_force_microscopy
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Atomic Force Microscope
http://files.ca
mpus.edublo
gs.org/blog.n
us.edu.sg/dis
t/3/2069/files/
2012/03/afmr3jgkw.gif
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Main AFM Techniques
• Contact Mode
– Tip slides across the surface
– Provides highest resolution, but may damage the
surface
• Non-contact Mode
– An oscillating tip is scanned 1 to 10 nm above the
sample’s surface
– Surface forces (capillary, electrostatic) affect tips’
resonant frequency
• Tapping Mode (Most Commonly Used)
– Similar to Non-contact, but at the largest deflection
the tip touches (taps) the surface, improving
resolution vs Non-contact mode
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AFM’s Atomic Resolution
http://www.eng.utah.edu/~lzang/images/Lecture_10_AFM.pdf
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AFM’s Atomic Resolution
AFM scans of gold structures sputtered for 75,
200 and 400 s on glass substrate before (RT)
and after annealing (300C). The average
surface roughness in given in nm.
V. Švorčík, O. Kvítek, O. Lyutakov, J. Siegel, Z.
Kolská, “Annealing of Sputtered Gold NanoStructures”. Appl. Phys. A 102747751 (2011)
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Comparison of STM and AFM
• STM works on conductive samples, while AFM can
work on both, conductive samples and insulators
• STM measures tunneling current, AFM measures
forces
• STM is non-contact, while AFM’s probe often makes a
direct contacts with the sample’s surface
• STM works in high vacuum, AFM can operate in liquid
and gas environment
• STM and AFM have comparable resolutions
• AFM has been adopted on a much wider scale than
STM
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Other Proximal Probe Microscopes
• Recently more local scanning probe tools have been
developed where their resolution does not depend on
the diffraction limit of conventional microscopy
• These probes include:
–
–
–
–
–
–
–
STMs
AFMs
Scanning Electrochemical Microscopes (SECMS)
Scanning Thermal Microscopes
Scanning Capacitance Microscopes
Magnetic Force Microscopes
Scanning pH probes
• Proximal Probes Can Be Used For Surface Modification
– Proximal Lithography
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Electrical Field-Induced Chemical
Modification: Oxidation
• Upon the application of small bias
(typically between 2V and 20 V) an
electrochemical oxidation take place
under the proximal probe – can be
applied to semiconductors and metals
• This oxide can be used to pattern the
substrate in several ways:
Top: AFM-tip-induced oxide pattern on Si
(100). Tip bias −10 V. Bottom: After
etching the oxide for 15 s using 50:1
aqueous HF solution. Ph. Avouris, R.
Martel, T. Hertel, R. Sandstrom, “AFM-tipinduced and current-induced local
oxidation of silicon and metals”, Appl.
Phys. A 66, S659–S667 (1998)
– Oxide can be used as a mask to etch the
unprotected substrate
– In forming the oxide, some of the substrate
material was converted to the oxide (i.e.
Silicon  Silicon Oxide), so removing the
resulting oxide will leave the groove where
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the oxide used to be
•
Electrical Field-Induced Chemical
Modification: Self-Assembled Monolayer
Resist Desorption
Au(111) substrate is coated with a
self-assembled n-alkanethiol
ultrathin (~2.5 nm) monolayer (SAM)
• The resist was etched by an STM tip,
producing 60 nm x 60 nm wells
Claudia B. Ross, Li Sun, and Richard M. Crooks, Langmuir
1993, 9, 632-636
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Electrical Field-Induced
Chemical Modification:
Multilayered Resist System
• Multilayered resist allows for translation of
SAM patterning to a more robust oxide
mask to produce 50 nm lateral features
• Octadecylsilyl SAM 2 nm thick
• Amorphous Si – conductive layer
• Si etch tetramethylammonium hydroxide
• Si Oxide Etch HF
Hiroyuki Sugimura, Osamu Takai, and Nobuyuki
Nakagiri, Journal of Vacuum Science & Technology
B 17, 1605 (1999)
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Scanning Probe Lithography
vs E-beam Lithography
K. Wilder, C. F. Quate, B. Singh, and D. F. Kyser,
“Electron beam and scanning probe lithography: A
comparison”, Journal of Vacuum Science &
Technology B 16„6 (1998)
• Both systems capable of
producing sub-50 nm features
• SPL is more tolerant to
exposure variations
• SPL uses lower energy and thus
has lower backscattering
• Use of ultrasharp (< 10 nm tip)
emitters [CNTs, molibdenum,
etc.] can allow for more
focused beam, larger gap
separation and higher writing
speeds for SPL
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Scanning Probe Lithography:
Sub 10 nm lateral resolution
• C-Methylcalix
[4]resorcinarene (C-MC4R)
molecular resist
• Writing speed 1-10 m/s
Marcus Kaestnera and Ivo W. Rangelow, “Scanning proximal probe lithography for sub-10 nm resolution
on calix[4]resorcinarene”, Journal of Vacuum Science & Technology B 29, 06FD02 (2011)
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Scanning Probe Lithography:
Sub 10 nm lateral resolution
Marcus Kaestnera and Ivo W. Rangelow, “Scanning proximal probe lithography for sub-10 nm resolution
on calix[4]resorcinarene”, Journal of Vacuum Science & Technology B 29, 06FD02 (2011)
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Mechanical Proximal Probe
Methods: Scratch Lithography
AFM phase image (right) of
nanolithographically etched
polycarbonate, 5µm scan of Pablo
Picasso’s "Don Quixote“
(www.asylumresearch.com)
• AFM tip is ploughed over the
surface of the substrate
• Features as small as 20 nm
are possible
• Possible to use SAM resists
to increase resolution
• Tips wear and break
• Heated tips can be used to
soften polymer surface for
patterning
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Mechanical Proximal Probe
Methods: Scratch Lithography
• Nanopatterning on silicon
surface using AFM
• 21 nm lateral resolution is
achieved
Xiaohong Jiang et al., “Nanopatterning on silicon surface using
atomic force microscopy with diamond-like carbon (DLC)-coated
Si probe”, Nanoscale Research Letters, 6:518 (2011)
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Mechanosynthesis
• Strong electric field (~2V/Å) in the vicinity of the probe
tip allow for sliding atoms over the surface (parallel
processes) and picking and placing atoms
(perpendicular processes)
• In November 1989 Don Eigler and his IBM Almaden
Research Center teammates spelled tiniest IBM logo
with 35 Xe atoms on Ni (110) surface.
researcher.ibm.com
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Mechanosynthesis
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Mechanosynthesis
• Besides Xe on Ni, CO on Pt, Pt and Pt,
Au on NiAl, Ag on Au surface and few
other systems have been successfully
demonstrated
4 Pt atoms spaced on
Pt(111) surface and 7 Pt
atoms crowded together.
From Joseph A.
Stroscio; D. M. Eigler,
“Atomic and Molecular
Manipulation with the
Scanning Tunneling
Microscope”
Science, 254(5036),
1319-1326 (1991)
OU logo and “smiley” produced via STM manipulation of Ag atoms on Au
substrate. Saw-Wai Hla, “Scanning tunneling microscopy single atom/molecule
manipulation and its application to nanoscience and technology”, Journal of
Vacuum Science & Technology B 23, 1351 (2005)
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Major Drawback of Proximal Probe
Lithography: “Are We There Yet?”
• It took researchers 1 week to position 35 atoms
of Xe on Ni substrate
• How long will it take to create 10 micron long,
1 micron wide, 0.5 micron high line
(approximately 1016 atoms) if the assembly
proceeds at a similar pace?
• The answer: More than 5,000 Billion Years. For
comparison, the age of the Universe is less than
4 Billion Years
• We need massively parallel processes to create
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anything from the bottom up
IBM’s Millipede System
• Prototype of
IBM storage
Millipede
data storage
device had
4,000 AFM
tips for
storing and
reading data
on a plastic
substrate
From E. Gnecco, “Nanotechnology: A gentle jackhammer”, Nature 461, 178179 (2009).
Scale bar is 40 microns
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Dip Pen Nanolithography (DPN)
Richard D. Piner, et al., "Dip-Pen"
Nanolithography, Science 283, 661 (1999)
• Invented by Chad Mirkin
(Northwestern University) in
1999.
• Water accumulates on AFM
tip and creeps onto surface,
reducing resolution of AFM
measurements
• We can use “inks” on AFM tip
to write spots and lines on
the surface
• Lines as thin as 15 nm
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Dip Pen Nanolithography
30 nm wide ODT line. Richard D. Piner, et al.,
"Dip-Pen" Nanolithography, Science 283, 661
(1999)
• Organic ink used most often
with DPL – 1-octadecanethiol
(ODT) on gold
• Many different inks/substrates
combinations are possible
• Resolution depends on grain
size of the substrate, contact
time/writing speed, humidity,
• It’s feasible to integrate
microfluidic technology for
wetting the tips
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Dip Pen Nanolithography:
Massively Parallel Pen Array
• To offset the drawback of
slow processing of DPL the
massively parallel 55,000
tip array has been
constructed.
• The complete patterning
took less than 30 min.
Top: Section of 55,000 tip array.
Bottom: AFM image of a miniaturized replica of the
face of the five-cent coin generated by depositing 1octadecanethiol on a gold-on-SiOx substrate followed
with chemical etching. The background is an optical
micrograph of a representative region of the substrate
on which the approximately 55,000 duplicates were
generated. From: ACS Nano, 1(2), 79–83 (2007)
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DPN: Protein Nanoarray Construction
• DPN can be used to
construct protein
nanoarray with several
types of proteins on the
same array (proof-ofconcept study – lysozyme
(Lyz) and rabbit
immunoglobulin-gamma
(IgG)).
• Startup NanoInk
commercializes DPN
technology
Ki-Bum Lee, Jung-Hyurk Lim, and Chad A. Mirkin, “Protein Nanostructures Formed via DirectWrite Dip-Pen Nanolithography”, J. Am. Chem. Soc., 125, 5588-5589 (2003)
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Thermal DPN (tDPN)
• Developed by William King
(Georgia Tech) and Lloyd
Whitman (Naval Research Lab)
• Use solid inks – limit evaporation
and run-off of the ink, result in
sharper features
• Use heated tips and inks such as
octadecylphosphonic acid that
melts around 100C
• Can be used in vacuum
environment (thus compatible
with conventional semiconductor
manufacturing)
P. E. Sheehan, L. J. Whitman, William P. King, and Brent A. Nelson, “Nanoscale deposition of solid inks via
thermal dip pen nanolithography”, Appl. Phys. Lett. 85, 1589 (2004)
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Near-Field Scanning Optical
Microscope (NSOM)
• Optical microscopy has a number of advantages (nondestructive, fast, reliable, low-cost, etc.)
• Abbe’s diffraction limit is around 200 nm (while a
resolution that is typically achieved with conventional
optical microscopy is lower)
• Near-field optical microscopy (probe-surface separation
of a few nanometers) can achieve resolution of 30 nm
• Optical glass fiber is pulled, tapered and coated on the
sides with Al
• The idea was first voiced by E. H. Singe in 1928 and
demonstrated in 1972 by Ash and Nichols (microwave
spectrum) and in 1984 by D. W. Poole and colleagues
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(in the visible spectrum)
Near-Field Scanning Optical
Microscope
http://www.olympusmicro.com/primer/techniques/nearfield/
High-resolution NSOM micrograph of a
3O-nm Ta film with lOO-nm holes.
Dörig, Pohl, and Rohner, J. Appl.
Phys., Vol. 59, No. 10, 15 May 1986
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Apertureless Near-Field Scanning
Optical Microscope(ANSOM)
L. Novotny and S. J.
Stranick, “Near-Field
Optical Microscopy and
Spectroscopy with Pointed
Probes”, Annu. Rev. Phys.
Chem. 57:303–31 (2006)
• Use sharp tip to scatter
oblique incident light
• The main limit to
resolution is the
sharpness of the tip
• Resolution of up to 10
nm has been achieved
10 m by 10 m ANSOM micrograph of the 20 nm
high waveguide from Gomez et. al., “Apertureless
scanning near-field optical microscopy: a comparison
between homodyne and heterodyne approaches”, J.
Opt. Soc. Am. B, 23 (5), 2006
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•Questions ?
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