09-08-2012, 12:59 PM
Micro-Machining
micromachining.pdf (Size: 3.08 MB / Downloads: 89)
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 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
Wet Etching Process Description
• The wet etching process involves:
– Transport of reactants to the surface
– Surface reaction
– Transport of products from surfaces
• The key ingredients are:
– Oxidizer (e.g. H2O2, HNO3)
– Acid or base to dissolve the oxidized surface
(e.g. H2SO4, NH4OH)
– Dilutent media to transport the products
through (e.g. H2O)
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.
Mechanical Micromachining
• Lithography and/or etching methods not
capable of making true 3D structures e.g.
free form surfaces
• Also, limited in range of materials
• Mechanical machining is capable of
making free form surfaces in wide range of
materials
• Can we scale conventional/non-traditional
machining processes down to the micron
level? Yes!
micromachining.pdf (Size: 3.08 MB / Downloads: 89)
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 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
Wet Etching Process Description
• The wet etching process involves:
– Transport of reactants to the surface
– Surface reaction
– Transport of products from surfaces
• The key ingredients are:
– Oxidizer (e.g. H2O2, HNO3)
– Acid or base to dissolve the oxidized surface
(e.g. H2SO4, NH4OH)
– Dilutent media to transport the products
through (e.g. H2O)
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.
Mechanical Micromachining
• Lithography and/or etching methods not
capable of making true 3D structures e.g.
free form surfaces
• Also, limited in range of materials
• Mechanical machining is capable of
making free form surfaces in wide range of
materials
• Can we scale conventional/non-traditional
machining processes down to the micron
level? Yes!