04-08-2012, 11:46 AM
Micro-Machining
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Micromachining Basics
• Refers to techniques for fabrication of
3D structures on the micrometer scale
• Applications include MEMS devices
e.g. airbag sensor, medical devices,
micro-dies and molds, etc.
• Most methods use silicon as substrate
material
Photolithography
• Used in
microelectronics
fabrication
• Used to pattern
oxide/nitride/polysilicon
films on silicon
substrate
• Basic steps
photoresist development
- Etching
- Resist removal
Photolithography Process Description
• The wafers are chemically cleaned to remove particulate matter,
organic, ionic, and metallic impurities
• High-speed centrifugal whirling of silicon wafers known as "Spin
Coating" produces a thin uniform layer of photoresist (a light
sensitive polymer) on the wafers
• Photoresist is exposed to a set of lights through a mask often made
of quartz
• Wavelength of light ranges from 300-500 nm (UV) and X-rays
(wavelengths 4-50 Angstroms)
• Two types of photoresist are used:
– Positive: whatever shows, goes
– Negative: whatever shows, stays
Bulk Micromachining
• Process for producing 3D MEMS
structures – older process
• Uses anisotropic etching of single crystal
silicon
• Example: silicon cantilever beam for
atomic force microscope
Surface Micromachining
• Newer process for producing MEMS
structures
• Uses etching techniques to pattern microscale
structures from polycrystalline (poly)
silicon, or metal alloys
• Examples: accelerometers, pressure
sensors, micro gears and transmissions,
micro mirrors etc.