Paavai Institutions Common to BME and MDE
UNIT-I
MEMS MATERIALS AND FABRICATION
1
,Paavai Institutions Common to BME and MDE
S.No Name of the content
1 Introduction
1.1 Typical MEMS and Microsystems
1.2 Materials for MEMS
1.3 Active substrate materials
1.3.1 Silicon as a substrate Material
1.4 Silicon and its compounds
1.4.1 Silicon dioxide
1.4.2 Silicon Carbide
1.4.3 Silicon Nitride
1.5 Silicon Piezo Resistors
1.5.1 Gallium Arsenide
1.5.2 Quartz
1.5.3 Polymers
1.6 Micromachining
1.6.1 Photolithography
1.6.2 Thin film deposition
1.6.3 Doping
1.6.4 Etching
1.7 Bulk machining
1.8 Wafer bonding
1.9 LIGA
Questions
2
,Paavai Institutions Common to BME and MDE
TECHNICAL TERMS
Anisotropic etch – this etch is highly directional. The etch rate varies with direction resulting in
straight or sloped sidewalls.
Aspect ratio - The height of an etched feature divided by its width in the case of a tall structure, or
the width divided by the depth in the case of a channel.
Bulk etch - A subtractive process in which the silicon substrate is selectively removed in relatively
large amounts.
Bulk Micromachining - A process that defines structures by selectively removing or etching inside
a substrate. This results in deep channels, or large, free-standing structures.
Chemical Mechanical Polishing (CMP) – A process used to flatten the topography of the wafer’s
surface as new layers are deposited.
Deposition - A process that deposits a material onto an object. Typically, thin films are deposited in
Microsystems fabrication using chemical vapor deposition, physical vapor deposition (evaporation)
or even oxide growth.
Electroforming – A process used to coat an object with a metal or metal alloy. This process uses a
positive and negative electrode submerged in an electrolyte solution. This is similar to
electroplating but provides for thicker coatings. The resulting structures are often used as a stamp or
mold used in hot-plastic embossing or injection molding, respectively.
Electroplating - The process of using electrical current to coat an electrically conductive object
with a layer of metal. The film is typically much thinner than what is done in electroforming.
Isotropic Etch – Etching is done at the same rate in all directions. Resulting structures have
concave cross-sections, bowl-shaped.
LIGA (Lithography, Galvanoformung, and Abformung) - An additive, lithographic process
which allows for the fabrication of complex, three dimensional structures with very high aspect
ratios exceeding 100:1.
4
, Paavai Institutions Common to BME and MDE
Oxidation - The process used to grow a uniform, high quality layer of silicon dioxide (SiO2) on
the surface of a silicon substrate.
Photolithography - The transfer of a pattern or image from one medium to another, as from a
mask to a thin film deposited on a silicon wafer.
Release etch – An etch process designed to remove material (sacrificial layer or bulk material)
from underneath the structural layer without affecting the structural layer itself. The removed
sacrificial layers provide space so the mechanical parts can move.
Sacrificial Layer - A layer deposited between structural layers for mechanical separation and
isolation. This layer is removed during a "release etch" to free the structural layers and to allow
mechanical devices to move. (Silicon dioxide, photoresist, polycrystalline silicon)
Structural Layer - A layer having the mechanical and electrical properties needed for the
component being constructed. (doped polycrystalline silicon, silicon nitride, some metals such
as chrome, gold and aluminum-copper)
Surface micromachining - A micromachining process that uses layers of thin films deposited
on the surface of a substrate to construct structural components for MEMS.
X-ray – A form of electromagnetic radiation having a wavelength in the range 0.01 nanometer
(nm) to 10 nm.
4
UNIT-I
MEMS MATERIALS AND FABRICATION
1
,Paavai Institutions Common to BME and MDE
S.No Name of the content
1 Introduction
1.1 Typical MEMS and Microsystems
1.2 Materials for MEMS
1.3 Active substrate materials
1.3.1 Silicon as a substrate Material
1.4 Silicon and its compounds
1.4.1 Silicon dioxide
1.4.2 Silicon Carbide
1.4.3 Silicon Nitride
1.5 Silicon Piezo Resistors
1.5.1 Gallium Arsenide
1.5.2 Quartz
1.5.3 Polymers
1.6 Micromachining
1.6.1 Photolithography
1.6.2 Thin film deposition
1.6.3 Doping
1.6.4 Etching
1.7 Bulk machining
1.8 Wafer bonding
1.9 LIGA
Questions
2
,Paavai Institutions Common to BME and MDE
TECHNICAL TERMS
Anisotropic etch – this etch is highly directional. The etch rate varies with direction resulting in
straight or sloped sidewalls.
Aspect ratio - The height of an etched feature divided by its width in the case of a tall structure, or
the width divided by the depth in the case of a channel.
Bulk etch - A subtractive process in which the silicon substrate is selectively removed in relatively
large amounts.
Bulk Micromachining - A process that defines structures by selectively removing or etching inside
a substrate. This results in deep channels, or large, free-standing structures.
Chemical Mechanical Polishing (CMP) – A process used to flatten the topography of the wafer’s
surface as new layers are deposited.
Deposition - A process that deposits a material onto an object. Typically, thin films are deposited in
Microsystems fabrication using chemical vapor deposition, physical vapor deposition (evaporation)
or even oxide growth.
Electroforming – A process used to coat an object with a metal or metal alloy. This process uses a
positive and negative electrode submerged in an electrolyte solution. This is similar to
electroplating but provides for thicker coatings. The resulting structures are often used as a stamp or
mold used in hot-plastic embossing or injection molding, respectively.
Electroplating - The process of using electrical current to coat an electrically conductive object
with a layer of metal. The film is typically much thinner than what is done in electroforming.
Isotropic Etch – Etching is done at the same rate in all directions. Resulting structures have
concave cross-sections, bowl-shaped.
LIGA (Lithography, Galvanoformung, and Abformung) - An additive, lithographic process
which allows for the fabrication of complex, three dimensional structures with very high aspect
ratios exceeding 100:1.
4
, Paavai Institutions Common to BME and MDE
Oxidation - The process used to grow a uniform, high quality layer of silicon dioxide (SiO2) on
the surface of a silicon substrate.
Photolithography - The transfer of a pattern or image from one medium to another, as from a
mask to a thin film deposited on a silicon wafer.
Release etch – An etch process designed to remove material (sacrificial layer or bulk material)
from underneath the structural layer without affecting the structural layer itself. The removed
sacrificial layers provide space so the mechanical parts can move.
Sacrificial Layer - A layer deposited between structural layers for mechanical separation and
isolation. This layer is removed during a "release etch" to free the structural layers and to allow
mechanical devices to move. (Silicon dioxide, photoresist, polycrystalline silicon)
Structural Layer - A layer having the mechanical and electrical properties needed for the
component being constructed. (doped polycrystalline silicon, silicon nitride, some metals such
as chrome, gold and aluminum-copper)
Surface micromachining - A micromachining process that uses layers of thin films deposited
on the surface of a substrate to construct structural components for MEMS.
X-ray – A form of electromagnetic radiation having a wavelength in the range 0.01 nanometer
(nm) to 10 nm.
4
