Types of Nanolithography
Types of Lithography
• A. Photolithography (optical,
• B. E-beam/ion-beam/Neutral
atomic beam lithography
• C. X-ray lithography
• D. Interference lithography
• E. Scanning Probe
F. Step Growth
G. Soft Lithography
I. Shadow Mask
Nuclear-track etched membrane
• KrF λ=248nm
• ArF λ=193nm
• F2 λ=157nm
II-B. Electron-Beam Lithography
• Exposure source: electron beam
• At acceleration voltage Vc=120kV, λ=0.0336Å
• Utilizes an electron column to generate focused
• Magnification x Resolution in (Å) = 107
for a 1mm feature on the image
• Charging effect - coating
• Escape depth
metal ~40 Å
semiconductor ~100 Å
insulator ~300 Å
E – Beam Writing
Direct writing, no mask needed
Arbitrary size, shape, order
slow, small area
conducting, no high T process
Sample E-beam Writing
Application of e-beam resist (PMMA)
Spin coating & soft bake
Ag paint reference, position
Tuning emission current
Shutting down SEM
II-C. X-ray Lithography
• Exposure source: x-ray (synchrotron)
• Resist: sensitive to x-ray (PMMA)
– IBM used resists developed for DUV and obtained successful
• Mask: SiC membrane covered by high Z metal;
• Advantages: High resolution
• Large area
• Disadvantage: Synchrotron facility necessary
fabricated by e –
X- Ray Lithography: Applications
• IC industry
– Proposed for fabricating Gigabit-level DRAM
– Not a mainstream technique for IC fabrication
• MEMS applications
• – LIGA
• – High aspect ratio devices
• Electron-beam lithography is currently the industry
standard for high-resolution, but has limited applications
due to its high cost and time-demanding process.
• X-ray lithography is an up-and-coming technology that
can be used in the same capacities as optical
lithography with better results. However, due to the high
cost of the equipment and supplies, as well as the desire
to push optical lithography to its absolute limit, we can
only say that x-ray lithography has a bright future ahead.
References for E – Beam and X –
C. Ngo and C. Rosilio, "Lithography for semiconductor technology," Nucl. Instr. and
Meth. In Phys. Res. B, vol. 131, pp. 22-29, 1997.
R. C. Jager, Introduction to Microelectronic Fabrication, vol. 5. Upper Saddle River,
New Jersey: Prentice Hall, 2002.
J. G. Chase and B. W. Smith, "Overview of Modern Lithography Techniques and a
MEMS Based Approach to High Throughput Rate Electron Beam Lithography," J.
Intell. Mater. Syst. Struct., vol. 12, pp. 807-817, 2002.
J. N. Helbert, Handbook of VLSI Microlithography. Norwich, NY: Noyes
Publications/William Andrew Publishing, LLC., 2001.
"Facility Procedures," in http://rlewb.mit.edu/sebl/facility_procedures.htm.
"Raith Nanolithography Products," in
"Electron Beam Lithography," in http://www.shef.ac.uk/eee/research/ebl.
K.-S. Chen, I.-K. Lin, and F.-H. Ko, "Fabrication of 3D Polymer Microstructures Using
Electron Beam Lithography and Nanoimprinting Technologies," J. Micromech.
Microeng., vol. 15, 2005.
• J. P. Silverman, "Challenges and Progress in X-ray Lithography," J. Vac. Sci.
Technol. B, vol. 16, pp. 3137-3140, 1998.
• S. Ohki and S. Ishihara, "An Overview of X-ray Lithography," Microelectron. Eng.,
pp. 171-178, 1996.
Focused Ion Beam (FIB)
• Liquid ion source: Ga, Au-Si-Be alloys LMI sources due
to the long lifetime and high stability.
• High exposure sensitivity: 2 or more orders of magnitude
higher than that of electron beam lithography
• Negligible ion scattering in the resist
• Low back scattering from the substrate
• Can be used as physical sputtering etch and chemical
• Can also be used as direct deposition or chemical
assisted deposition, or doping .
• Lower throughput, extensive substrate damage.
Neutral Atomic Beam Lithography
II-D. Interference Lithography
II-E. Scanning Probe Lithography
Two Different Modes of STM
• Constant current mode
• Constant height mode
Manipulation of Atoms
1. Parallel process
2. Perpendicular process
• Local anodic oxidation, passivation,
localized chemical vapor deposition,
electrodeposition, mechanical contact of
the tip with the surface, deformation of the
surface by electrical pulses
Diffusion of Atoms
Dip Pen Lithography
Thermal Dip Pen Lithography
Diagram illustrating thermal dip pen nanolithography. When the
cantilever is cold (left) no ink is deposited. When the cantilever is
heated (right), the ink melts and is deposited onto the surface.
(Journal of the American Chemical Society, 128(21) pp 6774 6775 , 2006)
Thermal Dip Pen Lithography
To perform the tDPN technique, the team employed a silicon cantilever that
contained a resistive heater and had a radius of curvature at its tip of about
100 nm. As the ink they used octadecylphosphonic acid (OPA), a material
that has a melting point of 99 °C and self-assembles into monolayers on
mica, stainless steel, aluminium and oxides such as titania and alumina.
Sheehan and colleagues coated the cantilever with OPA before heating it to
122 °C to melt the ink. Scanning the tip across a mica substrate laid down
98 nm wide lines of OPA.
The scientists were able to stop depositing molecules from the cantilever by
turning off the current supply to the resistive heater. That said, it took around
two minutes for the deposition process to stop, perhaps because of the low
thermal conductivity of the mica substrate.
The researchers believe that optimizing the technique, for example by
decreasing the radius of curvature of the cantilever tip, should enable them
to deposit features around 10 nm in size. So tDPN could find applications in
producing features too small to be formed by photolithography, as a
nanoscale soldering iron for repairing circuits on semiconductor chips, or for
making bioanalytical arrays. (Paul Sheehan, Lloyd Whitman, Applied
Physics Letters, Sep. 10, 2004)
Thermal Dip Pen Lithography –
• Whitman and colleagues Minchul Yang, Paul Sheehan and Bill King
deposited layers of the conducting polymer poly(3-dodecylthiophene)
(PDDT) onto silicon oxide surfaces. They produced nanostructures
with lateral dimensions of less than 80 nm and achieved monolayerby-monolayer thickness control – a monolayer of the molecules was
around 2.6 nm thick. The researchers were also able to control the
orientation of the polymer chains.
• PDDT has promise in the field of organic electronics and could have
applications in areas such as transistors, photovoltaic devices and
video displays. "The performance of these devices depends critically
on the degree of molecular ordering and orientation within the
polymer film, a property that has been difficult to control," said
Whitman. "We have succeeded in directly writing polymer
nanostructures with monolayer-by-monolayer thickness control
using tDPN. The deposition process employs highly local heating to
produce this polymer ordering and orientation."
A dip-pen nanolithography that has an array of 55,000 pens
that can create 55,000 identical molecular patterns
The background shows some of the 55,000 miniature images of a 2005 US
nickel made with dip-pen lithography. (Each circle is only twice the diameter
of a red blood cell.) Each nickel image with Thomas Jefferson's profile (in
red) is made of a series of 80 nm dots. The inset (right) is an electron
microscope image of a portion of the 55,000-pen array (Angewandte
Chemie 45 1-4, 2006 )