(AN OVERVIEW OF THE TECHNOLOGY)
Using the basic fundamental process namely Deposition process, lithography, and etching process the fabrication of micro mechanical components in various fields is lucidly present in this paper. Overall Micro-Electro-Mechanical-Systems (MEMS) is the integration of mechanical elements, sensors, actuators and electronics on a common silicon substrate through micro fabrication technology. MEMS devices are manufactured using batch fabrication techniques similar to those used for integrated circuits unprecedented levels of functionality, reliability and sophistication can be placed on a small silicon chip at a relatively low cost.
The main objective of this paper is to improvise and bring down the size of the equipment using the MEMS technology along with the Nanotechnology. The main advantage of MEMS is that the high performance of MEMS based fabricated equipment and to bring out at low prices. It is widely used along with nanotechnology in various fields like Biotechnology, Communications and Accelerometers.
2. MEMS processing
a) Deposition process
c) Etching process
3. Deposition process
a) Chemical Vapor Deposition (CVD)
b) Physical Vapor Deposition (PVD)
4. Advantages of MEMS
5. Applications in
Introduction to MEMS
MEMS revolutionize silicon based micro Micro-Electro-Mechanical-Systems
electronics with micro machining (MEMS) is the integration of mechanical
technology, making possible the elements, sensors, actuators &
realization of complete System-on-a –electronics on a Common silicon
chip. MEMS is an enabling technology substrate through microfabrication
allowing the development of smart technology. While the integrated circuit
products, augmenting the computational (IC) process sequences (e.g., CMOS,
ability of microelectronics with the Bipolar or BICMOS processes), the
perception and control capabilities of micro mechanical components are
microsensors and microactuators and fabricated using compatible
expanding the space of possible designs “micromachining” processes that
and applications. selectively etch away parts of the silicon
Microelectronic integrated wafer or add new structural layers to
circuits can be thought of as the “brains” form the mechanical and
of a system and MEMS augments this electromechanical devices.
decision making capability with eyes
and arms to allow Microsystems to sense
and control the environment. Sensors
gather information from the environment filtering, there by controlling the through measuring mechanical, thermal, environment for some desired outcome biological, chemical, optical and or purpose. Because MEMS devices are magnetic phenomena. The electronics manufactured using batch fabrication then process the information derived techniques similar to those used for from the sensors and through some integrated circuits unprecedented levels decision making capability direct the of functionality, reliability and actuators to respond by moving, sophistication can be placed on a small positioning, regulating, pumping and silicon chip at a relatively low cost.
materials on a substrate, to apply a MEMS Processing
patterned mask on the top of the films by Micro Electro Mechanical
photolithographic imaging and to etch Systems Technology is based on a
the films selectively to the mask. A number of tools and methodologies,
MEMS process is usually a structured which are used to form small structures
sequence of these operations to form with dimensions in micrometer scale
actual devices. (one millionth of a meter). Significant
1. Deposition process parts of the technology have been
2. Lithography adopted from integrated circuit (IC)
3. Etching process technology.
Deposition Process Almost all devices are built of
silicon which are realized in thin films of Ability to deposit thin films of materials and are patterned using materials is one of the basic building photolithographic methods like IC’s. blocks in MEMS process. Here we There are several processors that are not assume a thin film to have a thickness derived from IC technology and as the any where between a few nanometers technology continues the gap with IC about 100 micrometers. This film is technology also grows. locally etched using process described in
There are three basic building lithography and etching sections. blocks in MEMS technology, which are MEMS deposition technology the ability to deposit thin films of can be classified into two groups.
1. Chemical Vapor Deposition 300 ?c). The PECVD deposit the
(CVD) material on one side of the wafers on 1
2. Physical Vapor Deposition (PVD) to 4 wafers at a time where as LPCVD
systems deposit films on both sides of at
least 25 wafers at a time. Chemical Vapor Deposition
This process exploits the creation of solid materials directly from chemical reactions in gas and/or liquid compositions or with substrate materials. The solid material is usually not the only product formed by the reaction.
Byproducts can include gases, liquids
and even other solids.
In this process, the substrate is
placed inside a reactor to which a
number of gases are supplied. The Fig: typical hot-wall LPCVD reactor. principle is that a chemical reaction
takes place between the source gases.
The product of that reaction is a solid
Electrodeposition material with condenses on all surface
This process is also known as inside the reactor.
“Electroplating” and is restricted to The two important CVD
electrically conductive materials. There technologies in MEMS are Low Pressure
are electroplating and electroless plating CVD (LPCVD) and Plasma Enhanced
technologies. In the electro plating CVD (PECVD). The LPCVD process
process the substrate is placed in a liquid produces layers with uniformly thickness
solution (electrolyte). When an electrical and material characteristics, and the
potential is applied between a problem is high deposition temperature
conducting area on the substrate and a (>600 ?c) and also lower temperature (<
counter electrode (usually platinum) in
In any process, the surface of the the liquid, a chemical redox process
takes place resulting in the formation of substrate must have an electrically a layer of material on the substrate and conducting coating before the deposition usually some gas generation at the can be done.
counter electrode. Epitaxy
This technology is quite similar to
that of CVD process. If the substrate is
an ordered semiconductor crystal like
silicon, gallium arsenide it is possible
with this process to continue building on
the substrate with the same
crystallographic orientation with the
substrate acting as a seed for the
There are several technologies
for creating the conditions inside a Fig: Typical setup for Electrodeposition.reactor needed to support epitaxial
In the electroless plating process a growth of which the most important is more complex chemical solution is used, Vapor Phase Epitaxy (VPE).
in which deposition happens In this process a number of gases are spontaneously on any surface which introduced in an induction heater reactor forms a sufficiently high electrochemical where only the substrate is heated. The potential with the solution. This process temperature of the substrate typically is desirable since it doesn’t require any must be atleast 50% of the melting point external electrical potential contact to of the material to be deposited. the substrate during processing.The advantage of this process is it allows
The Electrodeposition process is the formation of films with considerable suited to make films (=1μm > 100μm) of thickness (>100μm). It is widely used metals such as copper, gold and nickel. for producing silicon on insulator (SOI) The deposition is best controlled when substrates and also for depositing silicon. used with an external electrical potential.
A schematic diagram of a typical vapor
phase epitaxial reactor is shown in figure.
Fig: Typical wafer oxidation furnace
Fig: Typical cold-wall vapor phase
epitaxial reactor It is typically used to form films
This process can be used to that are used for electrical insulation. form films of silicon with thicknesses of Physical Vapor Deposition (PVD)
(1μm to > 100μm). In this PVD there is no Thermal oxidation chemical reaction which forms the
This is a basic deposition material on the substrate. This is not process. It is oxidation of the substrate completely correct for casting processors, surface an oxygen rich atmosphere. This though it is more convenient to think of is also the only deposition technology them that way.
that consumes some of the substrate as it It covers deposition technologies proceeds. The growth of the film is in which material is released from source spurned by diffusion of oxygen in to the and transferred to the substrate. The two substrate. As the thickness of the most important technologies are oxidized layer increases the diffusion of evaporation and sputtering. PVD oxygen in to substrate becomes more comprises the standard technologies for difficult leading to a parabolic deposition of metals.
relationship between film thickness and Evaporation
oxidation time for films thicker than Here the substrate is placed 100nm. As it is a simple process it can inside a vacuum chamber in which a be used whenever we want. block of the material to be deposited is
also located .the source material is then
heated to boiling point. The vacuum is Sputtering
required to allow the molecules to It is a technology in which the evaporate freely in the chamber and then material is released from the source at condense on all surfaces. There are two much lower temperature than
popular evaporation technologies which evaporation. The substrate is placed in are e-beam evaporation and resistive the vacuum chamber with the source evaporation. In e-beam evaporation an material named a target and an inert gas electron beam is aimed at the source (argon) is introduced at lower pressure. material causing local heating and Glass plasma is struck using an RF evaporation. In resistive evaporation a power source causing the gas to become tungsten boat containing the source ionized.
material is heated electrically with a high The ions are accelerated towards current to make the material evaporate. the surface of the target causing atoms of A schematic diagram of a typical system the source material to break of from the for e-beam evaporation is shown in the target in vapor form and condense on all figure below. surfaces including the substrate. The
differences typically relate to the manor
in which the ion bombardment of the
target is realized. A schematic diagram
of a typical RF sputtering system is
shown in the figure below.
Fig: Typical system for e-beam
evaporation of materials
Fig: Typical RF sputtering system Advantages of MEMS and Nano Casting Manufacturing
In this process the material to be First MEMS and
deposited is dissolved in liquid form is a Nanotechnology are extremely diverse solvent. The material can be applied to technologies that could significantly the substrate by spraying or spinning. affect every category of commercial and Once the solvent is evaporated a thin military products.
film is evaporated a thin film of the MEMS and Nanotechnology are material remains on the substrate. This is already used for tasks ranging from in-particularly used for polymer materials dwelling blood pressure monitoring to which may be easily dissolved in organic active suspension system for solvents and is the common method used automobiles.
to apply photoresist to substrates. The nature of MEMS and
It is a simple technology Nanotechnology and its diversity of used for a variety of materials .some of useful applications make it potentially a the materials such as polyimide and far more pervasive technology than even spin-on-glass is applied on casting. integrated circuit microchips.
MEMS and Nanotechnology
allows complex electromechanical
systems to be manufactured using batch
fabrication techniques, decreasing cost
and increasing the reliability of the
sensors and actuators to equal those of
integrated circuits. Even though the
performance of MEMS and Nano
devices is expected to be superior to
macro scale components and systems, Fig: The spin casting process as used for the price is predicted to be much lower.
photoresist in photolithography
High frequency circuits will MEMS and Nanotechnology
benefit considerably from the advent of Applications
the RF-MEMS technology. Electrical
components such as inductors and There are numerous possible
tunable capacitors can be improved applications for MEMS and
significantly compared to their Nanotechnology. As a breakthrough
integrated counterparts if they are made technology, allowing unparalleled
using MEMS and Nanotechnology. With synergy between unrelated fields such as
the integration of such components, the biology and microelectronics, many new
performance of communication circuits MEMS and Nanotechnology
will improve, while the total circuit area, applications will merge, expanding
power consumption and cost will be beyond that which is currently identified
reduced. In addition, the mechanical or known. Here are few applications of
switch, as developed by several research current interest:
groups, is a key component with huge ; Biotechnology
potential in various microwave circuits. ; Communications
The demonstrated samples of ; Accelerometer
mechanical switches have quality factors 1) BIOTECHNOLOGY
much higher than anything previously
MEMS and Nanotechnology is
enabling new discoveries in science and
Reliability and packing of RF-
engineering such as the Polymerase
MEMS components seem to be the two Chain Reaction (PCR) Microsystems for
critical issues that need to be solved
DNA amplification and identification.
before they receive wider acceptance by
Micro machined Scanning
Tunneling Microscopes (STMs),
3) ACCELEROMETERS biochips for detection of hazardous
MEMS accelerometers are quickly chemical and biological agents and
replacing conventional accelerometers Microsystems for high-throughput drug
for crash air-bag deployment systems in screening and selection.
automobiles. The conventional approach 2) COMMUNICATIONS
reliable and are produced for a fraction uses several bulky accelerometers made
of discrete components mounted in the of the cost of the conventional macro
front of the car with separate electronics scale accelerometer elements.
near the air-bag (cost around $50).
MEMS and Nanotechnology has made it
possible to integrate the accelerometer
and electronics onto a single silicon chip
(at a cost between $5 to $10). These
MEMS accelerometers are such smaller,
more functional, lighter, and more
Hence, MEMS revolutionize silicon based micro electronics with micro machining technology, making possible the realization of complete System-on-a –chip.
Micro Electro Mechanical Systems Technology is based on a number of tools and methodologies, which are used to form small structures with dimensions in micrometer scale (one millionth of a meter).
MEMS is an enabling technology allowing the development of smart products, augmenting the computational ability of microelectronics with the perception and control capabilities of micro sensors and micro actuators and expanding the space of possible designs and applications.
Microelectronic integrated circuits can be thought of as the “brains” of a system and MEMS augments this decision making capability with eyes and arms to allow Microsystems to sense and controls the environment
In the present world, the technological revolution increasing at a rapid speed, hence the demand for manufacturing the goods to an improvised size at an effective performance is expected using the MEMS technology.