Transcript Physics 490N

Lithography
(and briefly, Electrodeposition)
ibm
bnl
UMass
manchester
July 10, 2008: Nano Education Institute at UMass Amherst
How do we control the shape
and size of nanostructures?
Self Assembly
(inspired by nature)
Lithography
(designed by humans)
Nanostructures
macroscale (3D) object
nanofilm,
or nanolayer (2D)
height
depth
width
nanowire,
nanorod, or
nanocylinder (1D)
nanoparticle,
nanodot,
quantum dot (0D)
Computer
Microprocessor
"Heart of the computer"
Does the "thinking"
Making Small Smaller
An Example: Electronics-Microprocessors
microscale
nanoscale
macroscale
ibm.com
Nanofilms
(making thin objects,
controlling the thickness)
An example of a FILM
A monolayer NANOFILM (single layer of molecules)
~1 nm thick
Langmuir film
This is an example of SELF-ASSEMBLY
Nanofilm by Electrodeposition
("electroplating")
I
V
cathode
Working
Electrode
(WE)
CuSO4 dissolved in water
anode
Counter
Electrode
(CE)
If using an inert Pt
electrode:
2 H2O –>
O2 + 4H+ + 4e-
"reduction"
Cu2+ + 2e- –> Cu(0)
"oxidation"
Cu(0) –> Cu2+ + 2e-
A nanofilm method,
Thermal Evaporation
Vaporization or sublimation of a
heated material onto a substrate
in a vacuum chamber
sample QCM
film
vapor
Au, Cr, Al, Ag, Cu, SiO, others
Pressure must be held low
to prevent contamination!
There are many other
thin film manufacturing
techniques
vacuum
~10-7 torr
source
resistive, e-beam, rf or laser
heat source
vacuum
pump
Nanofilms
(making thin objects)
From DOE
A Few Nanostructures Made at UMass
100 nm dots
18 nm pores
70 nm nanowires
12 nm pores
14 nm nanowires
13 nm rings
200 nm rings
14 nm dots
25 nm honeycomb
150 nm holes
Lithography
(controlling width and depth,
by using stencils, masks, & templates)
Lithography
Nanoscience
Rocks!
Rocks
(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
process recipe
spin coating
substrate
apply
spin
bake
spin on resist
resist
expose
mask (reticle)
exposed
unexposed
"scission"
develop
deposit
liftoff
narrow line
Lithography
IBM
Copper
Wiring
On a
Computer
Chip
Patterned
Several
Times
Patterned
Oxide
Other Uses
Ion implantation
substrate
silicon oxide
silicon
spin on resist
resist
dopant ions (e.g., B+, P+)
Etching
expose
mask
after
develop
etch
lift off
lift off
narrow trench
Positive and Negative Resists
Positive Resist
Negative Resist
resist
resist
expose
expose
scission
cross-linking
develop
develop
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
lens
contact
high resolution
proximity
extends mask life
projection
enables "stepping"
Resolution Limit of PL
How low can you go?
minimum linewidth
minimum pitch
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
Resolution in Projection Lithography
k1
R
NA
k1 ~ 0.4 - 1.1 (depends on materials, optics and conditions)
 is wavelength of light used
NA ~ 0.16 - 0.6 is the numerical aperture of the lens system

Rayleigh diffraction criterion—> 2bmin = 0.61/NA
is part of the underlying reason
With careful engineering, R ~/2 can be achieved
Contact Lithography
3 z
R
2 2
z is resist thickness
Down to 45 nm
Electron-Beam Lithography
Electron-Beam Lithography
Electron Beam
Polymer film
Silicon crystal
Nanoscopic Mask !
Down to 10 nm
CORE CONCEPT
FOR NANOFABRICATION
Deposition
Template
(physical or
electrochemical)
Etching
Mask
Remove polymer
block within cylinders
(expose and develop)
Nanoporous
Membrane
Down to 3 nm
Solar Cells
Benefit: Sun is an unlimited source of electronic energy.
Konarka
Electric Solar Cells
Made from single-crystal silicon wafers (conventionally)
Sunlight
wires
-
cross-sectional view
n-type silicon
Voltage
p-type silicon
+
-
Current
“load”
+
The load can be a lamp, an electric
motor, a CD player, a toaster, etc
Nanostructured Solar Cells
Sunlight
Voltage
More interface area - More power!
Current
“load”
+
Next....
....Electrodeposition