1. Scanning Probe Lithography (SPL)
CHEM *7530/750
Olivier Nguon
February 7th, 2006

2. Outlines Definition Scanning Probe Microscopes (SPMs)
Scanning Probe Lithography
Conclusions

3. Definition: Lithography
Greek Lithos: stone
“Printing process in which the image to be printed is rendered on a flat surface, and treated to retain ink while the nonimage areas are treated to repel ink.”
(The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2004)
"Girl with Flowers", Lithography by Angel Botello (1980)

4. Definition: Scanning Probe Lithography
Lithography using a sharp tip in proximity to a sample to pattern nanometer-scale features
Instrument:
Scanning Probe Microscope
100-nm-wide, 2-nm-thick spiral of polymer (poly(ethyl)amine)
(Lloyd Whitman, US Naval Research 1100)

5. Scanning Probe Microscope (SPMs)
Monitor local interactions between a tip and a sample
Physical, electrical or chemical information
Types of SPMs:
Scanning Tunneling Microscope
Atomic Force Microscope

6. SPMs: Scanning Tunneling Microscope
Voltage bias between tip and sample
Electrons tunnel between two electrodes
Current sensitive to the distance
_______________
Resolution: atomic scale
Vacuum needed
Substrate: conductive
Scanning tunneling microscope (Ludwig-Maximilians-Universität, München, W.M. Heckel)

7. SPMs: Atomic Force Microscope
Flexible cantilever with sharp tip
Forces between surface and tip detected by deflection
_____________
No vacuum needed
Non-conductive material allowed
(Helen G. Hansma, Department of Physics, University of California)

8. Others scanning probe technologies
Lateral Force Microscopy (LFM): surface friction and topography
Kelvin Probe Microscopy: contact potential difference
Scanning Capacitance Microscopy (SCM):2D carrier density; distribution of dopants

9. Scanning Probe Lithography
SPMs used to modify a sample surface:
Atomic Manipulation
Mechanical and Termomechanical Pattering
Local Oxidation
Electron Exposure of Resists

10.                                                       
1. Atomic Manipulation
SPM probe tip used to “push” or “pull” a particle
Push: Electric field and dipole moment of atom 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
(Jörn F. Lübben, EMPA swizerland)

11. 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

12. 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)

13. 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
Electron lithogaphy
K. Kobayashi Tokyo Institute of Technology

14. Conclusions Ability to pattern nanometer-scale features
Attracting method to semi-conductor industry
Limits
Throughput capabilities (coverage rates mm/s ->cm/s)
Future evolution
Carbon Nanotubes as scanning probes

15. References
C. F. Quate, H. Soh, Scanning Probe Lithography, Kluwer Academic Publishers, (2001). TK 7874 S
L. L. Sohn, Appl. Phys. Lett., 67, (1995).
J.A. Stroscio, Science, 254, , (1991).

16. 48 Fe atoms on a Cu (111) surface, Crommie et al., Science 1993
Thank you !!
48 Fe atoms on a Cu (111) surface, Crommie et al., Science 1993