Types of Nanolithography

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Types of Nanolithography

Types of Lithography


A. Photolithography (optical,
UV, EUV)


B. E
-
beam/ion
-
beam/Neutral
atomic beam lithography


C. X
-
ray lithography


D. Interference lithography


E. Scanning Probe


Voltage pulse


CVD


Local electrodeposition


Dip
-
pen



F. Step Growth

G. Soft Lithography

H. Nanoimprint

I. Shadow Mask

J. Self
-
Assembly

K. Nanotemplates


Diblock copolymer


Sphere


Alumina membrane


Nanochannel glass


Nuclear
-
track etched membrane

II
-
A. Photolithography



KrF λ=248nm


ArF λ=193nm


F
2

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
e
-
beam


Electron Column

Interaction Volume

SEM Resolution



Magnification x Resolution in (Å) = 107


for a 1mm feature on the image


Collimation


Wavelength


Charging effect
-

coating


carbon, metal


thickness


Escape depth


metal ~40 Å


semiconductor ~100 Å


insulator ~300 Å


SEM Images

E


Beam Writing


Advantages


Better resolution


Direct writing, no mask needed


Arbitrary size, shape, order



Disadvantages


Serial process


slow, small area


Compatibility


conducting, no high T process


Sample E
-
beam Writing
Procedure



Application of e
-
beam resist (PMMA)


Spin coating & soft bake


Loading


Ag paint reference, position


Power on


Tuning emission current


Stabilizing filament


Gun alignment


Adjust astigmatism


Referencing


Focusing


Writing


Shutting down SEM


Developing


Hard bake


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


results



Mask: SiC membrane covered by high Z metal; fabricated by e


beam writer



Advantages: High resolution


Large area


Disadvantage: Synchrotron facility necessary


X
-

Ray Lithography: Applications


IC industry




Proposed for fabricating Gigabit
-
level DRAM




Not a mainstream technique for IC fabrication


Nanoelectronics


MEMS applications




LIGA




High aspect ratio devices


Conclusions


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


Ray Lithography


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
http://www.raith.com/WWW_RAITH/nanolithography/nano_faqs2.html
.


"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.


Advantages:


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
assisted etch.


Can also be used as direct deposition or chemical
assisted deposition, or doping .


Disadvantages:


Lower throughput, extensive substrate damage.

Neutral Atomic Beam Lithography

II
-
D. Interference Lithography


Experiments

Patterned Nanostructures

II
-
E. Scanning Probe Lithography



Probe


STM, AFM


Techniques


Voltage pulse


CVD


Local electrodeposition


Dip
-
pen


STM

Two Different Modes of STM


Constant current mode


Constant height mode

AFM

Manipulation of Atoms

1.
Parallel process

2.
Perpendicular process

Nanolithography


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

Nanodeposition

Voltage Plus

STM CVD

Local Electrodeposition

AFM

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

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


Conducting Polymer


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 monolayer
-
by
-
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 )