Lithography(and briefly, Electrodeposition)

July 10, 2008: Nano Education Institute at UMass Amherst

bnl

manchester

ibm

UMass

How do we control the shape and size of nanostructures?

Lithography(designed by humans)

Self Assembly(inspired by nature)

Nanostructuresmacroscale (3D) object

widthdepth

height

nanofilm, or nanolayer (2D)

nanowire,nanorod, ornanocylinder (1D)

nanoparticle,nanodot,quantum dot (0D)

Computer

Microprocessor"Heart of the computer"

Does the "thinking"

Making Small SmallerAn Example: Electronics-Microprocessors

ibm.commacroscale

microscale

nanoscale

Nanofilms(making thin objects,

controlling the thickness)

A monolayer NANOFILM (single layer of molecules)

~1 nm thickLangmuir film

An example of a FILM

This is an example of SELF-ASSEMBLY

Nanofilm by Electrodeposition

VI

Cu2+ + 2e- –> Cu(0)

"reduction"

CuSO4 dissolved in water

Cu(0) –> Cu2+ + 2e-

"oxidation"

anodecathode

If using an inert Pt electrode:

2 H2O –> O2 + 4H+ + 4e-

WorkingElectrode(WE)

CounterElectrode(CE)

("electroplating")

A nanofilm method,Thermal Evaporation

Vaporization or sublimation of a heated material onto a substrate in a vacuum chamber

vacuum~10-7 torr

sample

source

film

vacuumpump

QCM

vapor

resistive, e-beam, rf or laserheat source

Pressure must be held low to prevent contamination!

Au, Cr, Al, Ag, Cu, SiO, others

There are many otherthin film manufacturingtechniques

Nanofilms(making thin objects)

From DOE

A Few Nanostructures Made at UMass100 nm dots 70 nm nanowires 200 nm rings

12 nm pores 14 nm dots

13 nm rings 25 nm honeycomb14 nm nanowires

18 nm pores

150 nm holes

Lithography(controlling width and depth,

by using stencils, masks, & templates)

Lithography

NanoscienceRocks

NanoscienceRocks

NanoscienceRocks!

(Using a stencil or mask)

Lithography: Basic concepts

Some possible desired features

narrow line narrow trench

modified substrate

•Photolithography•Electron-Beam Lithography•X-ray Lithography•Focused Ion-Beam Lithography•Block Copolymer Lithography

•Nano Imprint Lithography•Dip Pen Lithography•Interference Lithography•Contact Lithography•Others

Photolithography

Photolithography for Deposition

substrate

process recipe

spin on resist

resist

expose

mask (reticle)

develop

deposit

liftoffnarrow line

apply spin bake

spin coating

exposed unexposed

"scission"

Lithography

IBMCopperWiringOn aComputerChip

PatternedSeveral Times

Other Usesspin on resist

resist

expose

mask

develop

etch

lift off

dopant ions (e.g., B+, P+)

after

lift off

Ion implantation

substrate siliconsilicon oxide

PatternedOxide

narrow trench

Etching

Positive and Negative Resists

resist

expose

develop

Positive Resist

resist

expose

develop

Negative Resist

scission cross-linking

deposit & liftoff deposit & liftoff

exposed region results in presence of structure exposed region results in absence of structure (generally poorer resolution)

Several Types of Lithography

contact proximity projection

lens

high resolution extends mask life enables "stepping"

Resolution Limit of PLHow low can you go?

minimum linewidth There are actually many contributing factors that limit the minimum linewidth:• optical diffraction ()• resist sensitivity• depth of focus• purity of light source• numerical aperture of lens

minimum pitch

Resolution in Projection Lithography

€

R =k1λ

NA

k1 ~ 0.4 - 1.1 (depends on materials, optics and conditions) is wavelength of light usedNA ~ 0.16 - 0.6 is the numerical aperture of the lens system

Rayleigh diffraction criterion—> 2bmin = 0.61/NAis part of the underlying reason

With careful engineering, R ~/2 can be achieved

Contact Lithography

€

R =3

2

λz

2z is resist thickness

Down to 45 nm

Electron-Beam Lithography

Electron-Beam Lithography

Silicon crystal

Polymer film

Electron Beam

Nanoscopic Mask ! Down to 10 nm

CORE CONCEPT FOR NANOFABRICATION Deposition

Template

EtchingMask

NanoporousMembrane

Remove polymerblock within cylinders(expose and develop)

(physical orelectrochemical)

Down to 3 nm

Benefit: Sun is an unlimited source of electronic energy.

Solar Cells

Konarka

Electric Solar CellsMade from single-crystal silicon wafers (conventionally)

cross-sectional view

n-type silicon

p-type silicon

+

-

Sunlight

Voltage “load”

+

-

Current

The load can be a lamp, an electric motor, a CD player, a toaster, etc

wires

Nanostructured Solar Cells

+

-

Sunlight

Voltage “load”

CurrentMore interface area - More power!

Next....

....Electrodeposition