1. (and briefly, Electrodeposition)
Lithography
(and briefly, Electrodeposition)
bnl
ibm
UMass
manchester
July 10, 2008: Nano Education Institute at UMass Amherst

2. How do we control the shape and size of nanostructures?
Self Assembly
(inspired by nature)
Lithography
(designed by humans)

3. Nanostructures nanofilm, macroscale (3D) object or nanolayer (2D)
height
depth
width
nanoparticle,
nanodot,
quantum dot (0D)
nanowire,
nanorod, or
nanocylinder (1D)

4. Computer
Microprocessor
"Heart of the computer"
Does the "thinking"

5. Making Small Smaller An Example: Electronics-Microprocessors
microscale
nanoscale
macroscale
ibm.com

6. Nanofilms (making thin objects, controlling the thickness)

7. An example of a FILM A monolayer NANOFILM (single layer of molecules)
~1 nm thick
Langmuir film
This is an example of SELF-ASSEMBLY

8. Nanofilm by Electrodeposition
("electroplating") I V
cathode
anode
CuSO4 dissolved in water
Working
Electrode
(WE)
Counter
(CE)
Cu(0) –> Cu2+ + 2e-
"oxidation"
If using an inert Pt electrode:
2 H2O –>
O2 + 4H+ + 4e-
"reduction"
Cu2+ + 2e- –> Cu(0)

9. A nanofilm method, Thermal Evaporation
sample
QCM
Vaporization or sublimation of a heated material onto a substrate in a vacuum chamber
film
vapor
Au, Cr, Al, Ag, Cu, SiO, others
Pressure must be held low
to prevent contamination!
vacuum
~10-7 torr
source
There are many other
thin film manufacturing
techniques
resistive, e-beam, rf or laser
heat source
vacuum
pump

10. Nanofilms (making thin objects)

11. From DOE

12. A Few Nanostructures Made at UMass
100 nm dots
70 nm nanowires
200 nm rings
150 nm holes
18 nm pores
12 nm pores
14 nm dots
13 nm rings
25 nm honeycomb
14 nm nanowires

13. Lithography (controlling width and depth, by using stencils, masks, & templates)

14. Nanoscience Rocks! Nanoscience Rocks
Lithography
Nanoscience
Rocks!
Nanoscience
Rocks
(Using a stencil or mask)

15. Lithography: Basic concepts
Some possible desired features
narrow trench
narrow line
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

16. Photolithography

17. Photolithography for Deposition
process recipe
apply
spin
bake
spin coating
substrate
spin on resist
resist
expose
mask (reticle)
exposed
unexposed
"scission"
develop
narrow line
deposit
liftoff

18. Lithography Patterned Several IBM Times Copper Wiring On a Computer
Chip

19. Other Uses Patterned Oxide Ion implantation Etching narrow trench
substrate
silicon
silicon oxide
Patterned
Oxide
Other Uses
spin on resist
resist
Ion implantation
dopant ions (e.g., B+, P+)
Etching
expose
mask
develop
after
etch
lift off
narrow trench
lift off

20. Positive and Negative Resists
Positive Resist
Negative Resist
resist
resist
expose
expose
scission
cross-linking
develop
develop
deposit & liftoff
exposed region results in presence of structure
exposed region results in absence of structure
(generally poorer resolution)

21. Several Types of Lithography
lens
contact
proximity
projection
high resolution
extends mask life
enables "stepping"

22. Resolution Limit of PL How 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

23. Resolution in Projection Lithography
k1 ~ (depends on materials, optics and conditions)
is wavelength of light used
NA ~ 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
z is resist thickness
Down to 45 nm

24. Electron-Beam Lithography

25. Electron-Beam Lithography
Polymer film
Silicon crystal
Nanoscopic Mask !
Down to 10 nm

26. CORE CONCEPT FOR NANOFABRICATION Deposition Template Etching Mask
Nanoporous
Membrane
(physical or
electrochemical)
Remove polymer
block within cylinders
(expose and develop)
Down to 3 nm

27. Solar Cells Benefit: Sun is an unlimited source of electronic energy.
Konarka

28. Electric Solar Cells Sunlight - + + -
Made from single-crystal silicon wafers (conventionally)
Sunlight
wires -
cross-sectional view
“load”
n-type silicon
Voltage
p-type silicon + + -
Current
The load can be a lamp, an electric motor, a CD player, a toaster, etc

29. Nanostructured Solar Cells
Sunlight -
“load”
Voltage +
Current
More interface area - More power!

30. Next....
....Electrodeposition