nanolithography.pptx

7/29/2019 Nanolithography.pptx

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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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Top View Side View

1. Bead Coating(self-assembled monolayers)

2. Deposit Metal

3. Bead Removal

(toluene, tape)


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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!

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