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MICROELECTROMECHANICAL
SYSTEMS
( MEMS )
HARIKRISHNA SATISH.T
Introduction:
• MEMS stands for Micro-electromechanical systems, a
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manufacturing technology that enables the development of
electromechanical systems using batch fabrication techniques
similar to those used in integrated circuit (IC) design.
They can range in size from micrometers to millimeters
MEMS integrate mechanical elements, sensors, actuators and
electronics on a silicon substrate using a process technology
called micro fabrication.
Micro electro mechanical System (MEMS) is making and
combining of miniaturized mechanical and electrical
components on a common silicon substrate through micro
fabrication technology.
How MEMS work?
• The sensors gather information by measuring
mechanical, thermal, biological, chemical, magnetic and
optical signals from the environment.
• The microelectronic Ic’s act as the decision-making piece
of the system, by processing the information given by
the sensors.
• Finally, the actuators help the system respond by
moving, pumping, filtering or somehow controlling the
surrounding environment to achieve its purpose.
Manufacturing process:
• The MEMS materials:
• Primarily silicon its compounds
• other materials are quartz crystal, glass, metals such as aluminum,
titanium, tungsten and copper
• polymers such as photo resist.
• What is Micromachining ?
• Micromachining is a parallel (batch) process in which dozens to tens
of thousands of identical elements are fabricated simultaneously on
the same wafer.
• Divided into three major categories: basic, advanced, and
nonlithographic processes.
• Basic process flow in micromachining:
Figure : Illustration of the basic process flow in micromachining: Layers are deposited; photoresist
is lithographically patterned and then used as a mask to etch the underlying materials. The
process is repeated until completion of the microstructure.
 800C
BASIC PROCESS TOOLS
Deposition Process
Epitaxy: Epitaxy is a deposition method to grow a crystalline silicon
layer over a silicon wafer, but with a differing dopant type and
concentration
Impurity dopants
[AsH3 ; PH3]
(Controlled)
Silicon Contain source gas
[SiH4/SiCl4/SiH2Cl2]
Wafer Scale p-n junction for
Controlled electrochemical etching
High Temperature
( 800 C )
[Controlled]
Oxidation: High-quality amorphous silicon dioxide is obtained by
oxidizing silicon in either
dry oxygen or in steam at elevated temperatures (850º–1,150ºC)
850C 1150C
Si + O2/ Steam
SiO2
It is Depend on Temperature , Oxidizing environment and Time.
Sputter Deposition:
Evaporation
Al , Si, Ti,Cr , Al2O3
Heated at high Temperature
(Scanning at high voltage electronic beam)
Evaporation
(Water cooling of the target and
shielding from X-ray)
Condenses on a substrate
to form a film
CVD (Chemical Vapour Deposition)

Deposition Of Polysilicon :25 p.a -150 p.a
In CVD Chamber
SiH4
Si
+
2H2
600C  650C
Polysilicon may be grown directly with doping.

Deposition of Silicon dioxide :300C  500C
SiH4
+
O2
SiCl2H2
+
2N2O
Si(OC2H5)4 +
2N2O
SiO2
900C
SiO2
650C  750C
SiO2
+
+
2H2
2N2
+
2HCl
+ byproduct
High temperature
Oxide
Doped
Impurity
P2O5
Semiconductor
 Deposition of Silicon Nitrides
3SiH4
+
NH3
Si3N4
+
12H2
3SiCl2H2
+ 4NH3
Si3N4 + 6HCl + 6H2
2SiH4
+
N2
2SiNH
+
3H2
NH3
SiNH
+
3H2
SiH4
+
• Silicon nitride is common in the semiconductor industry for the passivation
of electronic devices because it forms an excellent protective barrier against
the diffusion of water and sodium ions
Photolithography
Photosensitive material
Selectively expose to Light
Non-exposed part
(remain same in physical properties)
Exposed part
(physical property change)
Perform Etching
Deposition of metal or
other thin film deposition

Etching: In etching, the objective is to selectively remove
material using imaged photoresist as a masking template.
Wet Etching :Anisotropic Wet Etching:
Dipped into
Substrate
KOH Solution
Removal of material
Depending on the
Crystallographic orientation
Electrochemical Etching
 Reactive Ion Etching ( RIE )
 Process of reactive ion etching.
Placed into
Substrate
Reactor
contain
several
gas
Plasma is struck in the mixture
Gas molecule into ions
React with the surface
of the material and etched
 Deep Reactive Ion Etching ( DRIE )
SF6 isotopic Etching
(SF6 & O2 etches the substrate)
C4F8 deposition
SF6 anisotropic etching
for floor cleaning
Using these processes some micromachining methods are
applied on silicon materials are:
• A) Bulk micromachining: Bulk micromachining designates
the point at which the bulk of the Si substrate is etched
away to leave behind the desired micromechanical
elements. The methods commonly used to remove excess
material are wet and dry etching, allowing varying degree
of control on the profile of the final structures.
• B) Surface Micromachining: The MEMS fabrication process
based on standard CMOS microelectronic processes. MEMS
structures are photo lithographically patterned in
alternating layers of deposited polysilicon and silicon
dioxide, and then are "released" by dissolving away the
silicon dioxide layers.
Applications of MEMS :
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inkjet-printer cartridges,
accelerometer,
miniature robots,
micro engines,
inertial sensors,
micro actuators,
optical scanners,
fluid pumps,
chemical, pressure and flow sensors.
Application in Radio frequency (RF)
Reference :• By Maluf Nadim and Williams Kirt .
An Introduction to Microelectromechanical Systems
Engineering.
• By committee on Advanced Material and Fabrication.
Microelectromechanical Systems.
• The MEMS Handbook.
Thank You