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
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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
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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