lithography techniques
TRANSCRIPT
Lithography Techniques
Piotr Matyba
Department of Physics
Umeå University
Outline
Motivation for micro and nanotechnology
Techniques for micro and nano patterning
Soft lithography
Photolitography
E-beam lithography
Ion-beam lithography
Future and possible development
Moore’s low
The complexity for minimum component costs has increased at a rate of roughly a factor of two per year ... Certainly over the short term this rate can be expected to continue, if not to increase. Over the longer term, the rate of increase is a bitmore uncertain, although there is no reason to believe it will not remain nearly constant for at least 10 years. That means by 1975, the number of components per integrated circuit for minimum cost will be 65,000. I believe that such a large circuit can be built on a single wafer. (Electronics Magazine, 19th April 1965)
Techniques for micro patterning
Add one more slide explain how it is done in practice
Typical flowchart for fabrication
substrate resist spinning
development
metal deposition
etchinglift off
exposure
electrolytic growth
Lithography
Reproduction of a pattern ↔ expose a resist to open windows in a controlled way
First planar technology (1957)
Photoresist
soluble
not soluble
Ideal photoresist
In contrary to photography one does not want any grayscale, the highest contrast is desired
Negative resist
Positive resist
Optical lithography by contact
Projection lithography
Evolution of projection lithography
Phase shifting masks (PSM)
The use of PSM techniques allows to go down to the Rayleight criterion, k=0.61 to k=0.4
85 nm gate with PSM
transmision phase shift
Resolution Enhanced Techniques
Nature, T. Ito & S. Okazaki
Film Thickness 60um, 10um posts6:1 aspect ratio structures
10µ line/space features 6:1 aspect ratio structures
193nm lithography
Extreme UV (EUV) lithography
EUV is absorbed by all materials, and gasses
vacuum required !Physikalisch-Technische Bundesanstalt, Annual Report 2002
Photons are not for ever !
reflection
refraction
Aberrations
- High surface figure
- Aspherization
Flare (contrast loss)
- Spatial frequency roughness
Reflectivity loss
- Graded multilayer thickness
Competition between immersion 157nm technology and EUV technology. The industry however seems to develop lens/immersion approach.
X-ray lithography
X-ray mask
Examples of X-ray lithography
+ Good resolution
- Complex and expensive
- Time demanding
3D X-ray lithography
Produces 3D structures, with potential application to photonic crystals
Electron beam lithography
Electron beam spot less than 10nm
Very small wavelength no diffraction limitation
Direct writing no mask needed
Resolution depends upon the photoresist, limitation ~1nm
Sequential writing, small throughput
Electron-resist interaction
Multilayer technique
E-beam writing
Schottky Emitter tip
Tungsten heating filament
Reservoir (ZrN)
Crystal W
Hard density track patterning on a real magnetic hard disk
Pitch ~60nm
50 nm gold dots on a silicon wafer
Ion beam litography
Holes in a silicone membrane
Trenching in GaAs
30kV Gallium ionsIon beam spot size <10nm
rapidly absorbed
Near field lithography (soft)
The pattern is reproduced by a mold or a stamp
Fast and efficient method
No scaling, 1:1 ratio
Future
Development of light based techniques for industrial applications (EUV range)
Further development of soft lithography techniques
Techniques based upon self assembling abilities of certain materials. Resolution below 1nm.
A huge effort put on a production of photo resistive materials with good properties for EUV lithography