Title: Microlithography for IC Production
1Microlithography for IC Production
- by John Broky
- OPTI 422
- 9/22/03
2What is Microlithography?
It is a form of printmaking in the micron range,
predominantly used for circuits on silicon
wafers.
It creates highly accurate 2-D patterns in
photosensitive resist material, which is used to
build integrated circuits.
3Integrated Circuits
- Complex circuitry that fits on semiconductor
microchips the size of a fingernail. The
circuitry consists of several layers stacked upon
each other where each layer contains an elaborate
network of connections just microns in size.
4Components of the Exposure System of a Typical
Stepper
- Lithographic Projection Lens
- Illumination Subsystem
- Wafer Positioning Subsystem
5Lithographic Projection Lens
- Contains many simple lens
elements - Images photomask with
demagnification 5x - Wavefront aberration must be
less than 1/10 the source
wavelength - Corrected for chromatic
aberration at 365nm
6Illumination Subsystem
- 1000 watt mercury arc lamp
- Layers of dielectric filters allow only
365nm light
through - Light passes through relay optics and is
projected through the
photomask and onto
the entrance pupil of the lithographic lens - Non-uniformity must be less than 1
- Photoresist is exposed to the image
for only a few
hundredths of a second
light
photomask
7Wafer Positioning Subsystem
- The position of the silicon wafer must be as
precise as the optics - Each wafer contains around 100 semiconductor
devices, or chips - Less than one second to move between successive
exposure sites - It detects and corrects tilt errors because the
wafer surface is not flat enough to guarantee
focus everywhere - A stepper can expose about 60 wafers in one hour
8Close-ups of Integrated Circuits
Pictures courtesy of www.charfaq.umn.edu
9Other Lithography Processes
- Optical Proximity Printing
- X-Ray Proximity Lithography
- Scanners
- Step-and-Scan
- Immersion Lithography
10References
- Sheats, James R., and Bruce W. Smith.
Microlithography Science and Technology. New
York Marcel Dekker, Inc, 1998. - http//www.charfac.umn.edu/MMS/ProjectMicro/Explor
ations/Jun1998.html - http//www.geocities.com/beatles_forever_plus_some
/Silicon_information.html - http//www.siliconstrategies.com/story/OEG20030422
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