1. NANO 101 Introduction to Nanotechnology
Lithography
NANO 101
Introduction to Nanotechnology

2. Lithography “Photoengraving” Photolithography
Transfer pattern into reactive polymer film (“resist”)
Use resist to replicate pattern into thin film or substrate
Photolithography
Electron beam lithography
X-ray lithography
Focused ion beam lithography
Lithography

3. Photolithography “Printing”
Transfer of the pattern using an optical technique
Resist = photoresist; photoactive polymer, positive or negative
Coat substrate with resist
Mask; expose with light
Develop (dissolve exposed OR unexposed areas with chemicals)
Etch unprotected areas or deposit layer of metal
Strip resist
Photolithography

4. Maximum resolution (minimum size) of individual features limited by diffraction
bending of light
around an edge
through a slit
past an object (edges)
direction changes
wavelength, frequency stay the same
Photolithography

5. Photolithography Maximum resolution: λ b s d b s d

6. Three Modes of Photolithography

7. Photolithography: Shadow Printing
Contact mode:
s = 0
Best resolution; near 100% accuracy
Maximum resolution rarely achieved
Substrate and resist film rarely completely uniform
Proximity mode:
Small gap between mask and substrate
Need extremely flat substrates and resist films

8. Photolithography: Projection Printing
Resolution
Worse resolution than shadow printing
Lens imperfections
Increased diffraction
type of resist material
optical system (apertures)
exposure wavelength (λ)
Best resolution ~ λ/2

9. Radiation with smaller wavelengths
Deep Ultra-Violet (DUV): λ < 300 nm
Need to use special lasers
Minimum pattern size ~ 100 nm
Extreme UV (EUV): λ = nm
Minimum pattern size ~ 60 nm
Strong absorption of light by lenses
Low reflectance of light by mirrors

10. Current State of EUV Sustained 100W average source power
1,000 wafers processed in 24 hrs

11. Other Options: ArF laser (193 nm) is current state of art
Immersion (change refractive index)
Double Patterning
Diffraction limit
n = index of refraction
n air : 1.0
n water: 1.3

12. Double Patterning

13. X-Ray Lithography X-Rays System 0.04 nm < λ < 0.4 nm Mask
X-ray absorbing material pattern on a thin X-ray transparent material
X-ray source
Bright enough in necessary wavelength range
Expensive
X-ray sensitive material

14. LIGA Lithography, Electroplating, Molding

15. Electron Beam Lithography
E-beam:
Finely focused beam of electrons (few nm dia.)
Electrons deflected accurately and precisely to “write” pattern without mask
Resolution
Diffraction not an issue
λ < 1 Å (0.1 nm)
Scattering
Forward (in resist layer)
Backwards (substrate)

16. Electron Beam Lithography
System
Electron source (gun)
Electron column (forms beam)
Mechanical stage
Control Computer

17. Focused Ion Beam (FIB) Lithography
Ions scatter much less than electrons
Sources:
Liquid metal ions (Ga; Au-Si-Be alloys)
Long lifetime, high stability
Resolution
sub-µm dimensions (~250 nm)
High resist exposure sensitivity
Negligible ion scattering in resist
Low back scattering from substrate
Extensive substrate damage
Also used for etching, deposition, and doping

18. Focused Ion Beam (FIB) Applications
Etching
Physical sputtering etching
Bombard areas to be etched with energetic ion beams
Simple, applicable to any sample material
Chemical etching
Chemical reactions between substrate surface and gas molecules adsorbed onto surface
Increased etching rate, little residual damage
Deposition
Direction deposition (low energy ions)
Chemical-assisted deposition

19. FIB – etching/deposition
Nano Factory Achieved by Focused Ion Beam Toshiaki Fujii, and Takashi Kaito, Microsc Microanal 11(Suppl 2), See more at:

20. FIB - Deposition
Deposition of Pt on Al substrate to form micro-grating for measuring material deformation

21. Soft Lithography Alternative to photolithography
Cheaper / more flexible
Printing of Self-Assembled Monolayers (SAMs)
Molding of liquid precursors
Techniques:
Microcontact printing
Nanoimprint

22. Microcontact Printing
“Stamp” made
Pour liquid polymer into a mold to make a “stamp”
Mold often made by photolithography
“Ink” the stamp
Dip into solution so SAM formed on surface of stamp
Stamp the substrate
Place the inked stamp on a substrate
SAM transferred to substrate in specific pattern

23. Microcontact Printing
Voskuhl, J., Wendeln, C., Versluis, F., Fritz, E.-C., Roling, O., Zope, H., Schulz, C., Rinnen, S., Arlinghaus, H. F., Ravoo, B. J. and Kros, A. (2012), Immobilization of Liposomes and Vesicles on Patterned Surfaces by a Peptide Coiled-Coil Binding Motif . Angew. Chem. Int. Ed., 51: 12616– doi:  /anie

24. Nanoimprint Make template Coat substrate with polymer
3. Press stamp into polymer at high temperature; polymer deforms
4. Cool polymer and pull stamp away
5. Polymer can be then be etched or used as is
D.R. Hines et al., Appl. Phys. Lett. 86 (16), (2005).

25. Nanomanipulation and Nanolithography
Based on Scanning Probe Microscopy (SPM) techniques
- can be used for molecular manipulation
Types of Scanning Probe Microscopy (SPM)
Scanning Tunneling Microscopy (STM)
Electrically conducting materials
Atomic Force Microscopy (AFM)
Dielectric (insulating) materials

26. Nanomanipulation STM with Tungsten tip Placed Xenon atoms on surface
UHV and low temperature
Clean environment and surface
Absence of thermal diffusion on surface
Nanomanipulation
D.M. Eigler and E.K. Schweizer, Nature 344, 524 (1990).

27. The World’s Smallest Movie

28. Nanomanipulation with AFM
Perpendicular Processes: atoms lifted, then dropped
Parallel Processes: atoms dragged along surface
Pushing
Pulling
Sliding
C. Baur, et al., Nanotechnology 9, 360 (1998).

29. SPM Nanofabrication Advantages Disadvantages
Nanoscale control in three dimensions, necessary for atomic manipulation
Manipulation and characterization
Disadvantages
Small scanning area
Slow scanning
Tips must be high quality and consistent
Surface must be flat and smooth
UHV and low temperatures
SPM Nanofabrication

30. Dip-Pen Nanolithography (DPN)
Works under ambient conditions
Scan tip across substrate, atoms or molecules move from AFM tip to substrate
“Water-filled capillary”
Chemisorption:
Made 15 nm dots, spaced ~5 nm apart to form an N (gold substrate)
Dip-Pen Nanolithography (DPN)
C. Mirkin, Northwestern Univ.

31. Polymer Pen Lithography
DPN + µCP
11 million pen array
Science 19 September 2008:vol. 321 no

32. Summary Photolithography Soft Lithography SPM-based techniques
Reaching size limits (diffraction, etc.)
Soft Lithography
Relatively new
Fabrication of nanostructrures and nanodevices
SPM-based techniques
Promise for using atoms and molecules as building blocks