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Nanolithography
M
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Introduction
Nanolithography is the branch of nanotechnology concernethe study and application of fabricating nanometer-scale strmeaning patterns with at least one lateral dimension betwesize of an individual atom and approximately 100 nm.Nanolithography is used during the fabrication of leading-edsemiconductor integrated circuits (nanocircuitry) or
nanoelectromechanical systems (NEMS).
As of 2012, nanolithography is a very active area of researchacademia and in industry.
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Resolution
NA
KR
1
K1 is the system constant
is the wavelength of the light
NA = 2 ro/D, is the numerical aperture
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State of art Lithography
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STM can move atoms around on a surface.
SPM Lithography
Iron on Copper Iron on Copper
Eigler, et al. fr
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Scanning Probe Lithogra
SPMs used to modify a sample surface:
1. Atomic Manipulation
2. Mechanical and Termomechanical Pattering
3. Local Oxidation
4. Electron Exposure of Resists
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1. Atomic Manipulation
SPM probe tip used to push or pull a
particle
Push: Electric field and dipole moment ofatom lead to potential energy gradient
Pull: Chemical binding force between tip
and atoms
or
Magnetic interactions
Pick-up of magnetic beads with the
magnetizable tip in the presence of an
external magnetic field
(Jrn F. Lbben, EMPA swizerland)
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Manipulation of Individual Atoms Us
STM Techniques
(a) Probe tip is maintained adistance from the surfacethat is sufficient to avoiddisturbing the adsorbedatom
(b) Probe tip is movedcloser to the surface so thatthe adsorbed atom isattracted to the tip
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Positioning single atoms with scanning tunnelling
microscope. Eigler, D. M. Nature 1990, 344, 6266
The scanning tunneling microscope (STM) at low temperature
(4K) to position 35 Xe atoms on a single-crystal Ni surface.
THIS IS FUN!!!
The entire
~ 3nm!
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Limitations of STM Manipulation
Must be carried out in a very high vacuum to prevstray atoms or molecules from interfering with theprocess
Surface of substrate must be cooled to temperaturnear absolute zero in order to reduce thermaldiffusion that would gradually distort the atomicstructure being formed
These limitations make STM manipulation of individualatoms and molecules very slow and expensive
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Commercial Nanomanipulator
NanoManipulator DP-100/200
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2. Local Oxidation
Voltage bias between probe tip and sample
Intense electric field
Local oxidation
Silicon: Growth of silicon oxide from crystal Si
Electric-field-enhanced oxidation
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3. Mechanical & Termomechanical
Patterning
Probe tip used to plough a soft layer
Heating of the tip to melt the layer
Mechanical patterning (Graham
Leggett, 2002)
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4. Electron Exposure of Resist
Electric bias between conductive probe tip
and sample
Field emission of electrons
Chemical changes induced (cross-linking,
scissions bonds, etc.)
Etching
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Local Electrodepositio
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Dip Pen Lithography
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Dip-Pen Lithography (DP
An alternative scanning probe technique that does show propractical applications
In DPN, the tip of an atomic force microscope is used to tranmolecules to a substrate surface by means of a solvent men
Process is analogous to using an old-fashioned quill pen to t
ink to a paper surface via capillary forces
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Dip-Pen Lithography
Tip of an atomic force microscope is used todeposit molecules through the water meniscusthat forms naturally between the tip and thesubstrate
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The grain size of the substrate
the texture of paper controls the resolution of conventional writing.
chemisorptions and self assembly can be used to limit the diffusion
the molecules after deposition.
The tip-substrate contact time and thus the scan speed
influence DPN resolution.
by controlling the rate of ODT transport from the tip to the substrate.
Relative humidity seems to affect the resolution of
the lithographic process
The size of the water meniscus that bridges the tip and substrate
depends on relative humidity
The resolution of DPN depends on
parameters:
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Dip Pen Lithography
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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
http://dx.doi.org/10.1021/ja0612807http://dx.doi.org/10.1021/ja0612807http://dx.doi.org/10.1021/ja0612807http://dx.doi.org/10.1021/ja0612807http://dx.doi.org/10.1021/ja0612807http://dx.doi.org/10.1021/ja0612807 -
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Nanosphere Lithography (NS
Metal (Au, Ag) Deposition
Array of
Polystyrene Beads
as Mask
Si Substrate
Metal deposit with
electron beam
evaporation (EBE
system
Control over shap
size of patterns b
varying bead radi
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Nanosphere Lithography (NS
Top View Side View
1. Bead Coating(self-assembled monolayers)
2. Deposit Metal
3. Bead Removal
(toluene, tape)
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Nanosphere Lithography (NS
Targeted Pattern
scanning electron microscopy (SEM)
image resulting from fabrication proces
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Soft lithographySoft lithography represents a non-
photolithographic strategy based on self
assembly and replica molding for carrying
out micro- and nanofabrication
1. Generate patterns and structures with
feature sizes ranging from 30 nm to
100 mm
2. Convenient, effective, and low-cost
Xia, Y. N. and Whitesides, G. M. Soft Lithograph
Annu. Rev. Mater. Sci.28, 153-184 (1998)
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Process Schematic
A prepoly
covering (1) is cur
or light a
demolde
an elasto
stamp (3
inked by
(4) or wit
pad (5) a
onto the
(6), form
assemblemonolaye
transferre
substrate
selective
Scanning
microgra
the mast
of the sta
the printe
etched p
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Good and Bad Examples:
Black linesdrawn tomark theedge of thesnowflakes
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Nano-Imprint Technology
Nanoimprintlithography patterns aresist by deforming the resist shapethrough embossing (with a mold),rather than by altering resist chemicalstructures through radiation (withparticle beams). After imprinting theresist, an anisotropicetching is used toremove the residue resist in thecompressed area to expose the
underneath substrate. 10nm diameterholes and 40nm pitch in PMMA can beachieved on Sior a metal substrate andexcellent uniformity over 1 square inch.
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Direct Nanoimprinting of Metal Nanoparticle
Ko, S. H., et. al, Nano letters, Vol. 7, No. 7, p1869, 2007
Step-and-Flash IMPRINT Lithogr
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Step and Flash IMPRINT Lithogr(SFIL)Commerical nanoimprinter: $0.5-
1.6M
Lower forces: 100 kPa
No heating, no cooling
Longer lifetime, faster imprint
Sub 5-nm demonstrated
Issues
Production of templatesDefect controlSmall throughput
Materials
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Magnetolithography
Nanostencil Lithography
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Nanostencil Lithography
Stencil lithography is a novel method of fabricating nanometer scale patterns using
nanostencils, stencils (shadow mask) with nanometer size apertures.
It is a resist-less, simple, parallel nanolithography process, and it does not involve anyheat or chemical treatment of the substrates (unlike resist-based techniques).
AFM Lithography
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AFM Lithography
The AFM tip is used to "bulldozethrough a top layer of resist.
Submersion in developer produc
undercut in the lower layer of re The top layer then serves as a sh
mask for deposition.
After removal of resist, the deponanostructure remains.
For nanocontact printing, the inistructuring is performed in paral
a contact mask.
AFM Bulldozing Developing
Depositing Lift Off
Undercut
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Thank You!