Download Nano/Micro Electro-Mechanical Systems (N/MEMS)

Nano/Micro Electro-Mechanical
Systems (N/MEMS)
Osama O. Awadelkarim
Jefferson Science Fellow and Science Advisor
U. S. Department of State
&
Professor of Engineering Science and Mechanics, and the
Associate Director for the Center for Nanotechnology
Education and Utilization, The Pennsylvania State
University, U. S. A.
• N/MEMS :Nano/Micro-Electro-Mechanical Systems.
• N/MEMS Comprises : A system which contains
sensors, actuators, and integrated circuits (IC)
processing units.
• N/MEMS device : A single device (e. g.
nano/microsensor or a nano/microactuator).
• Typical N/MEMS device size : In the range 100 nm to
1000 mm.
Measurement and Information System
N/MEMS System
N/MEMS AND/OR IC PROCESSES
MATERIAL FOR N/MEMS AND/OR ICs
Engineering Materials :
1) Metals.
2) Semiconductors.
3) Ceramics.
4) Polymers.
Electronic Materials :
- Comprise materials from all of the four engineering materials
categories.
- They have no common physical or chemical properties : their
electrical properties span the range from nearly-ideal insulators
to excellent conductors.
- They are important in IC and N/MEMS fabrication.
ELECTRONIC MATERIALS
• To fabricate ICs and N/MEMS many different kinds of bulk
materials and thin films are used.
• The bulk materials are predominantly semiconductors.
• The most important semiconductor for ICs and N/MEMS is Si.
• Thin films in ICs and N/MEMS are classified into four groups:
Thin films
thermal SiO2
Deposited SiO2
dielectrics
Poly-Si
Deposited Si3N4
metals
Metallization
- Metallization is a process whereby metal films
are formed on the surface of a substrate.
- The most common and important metallization
method is physical vapor deposition (PVD).
- The main PVD processes are evaporation and
sputtering.
Evaporation
Highlights of a Typical
Evaporation Process
- Open evaporator.
- Remove wafer holder.
- This is where the wafers will be during the evaporation process.
- Remove the bell jar.
- Prepare metal: e. g., use metal wire.
- The metal will be placed in a "basket".
- Some evaporators use a "coil" instead of a "basket".
- The basket/coil should be installed between the two electrodes,
and the metal placed inside the basket or around the coil.
- Move shutter to cover the filament.
- Lower pressure ( ~ 10-6 Torr ).
- Heat the filament to evaporate the metal.
- Cool and remove wafers.
- The test wafer allows measurement of film thickness.
LITHOGRAPHY
Lithography is the process of imprinting a geometric pattern from a mask onto a thin
layer of material called a resist which is a radiation sensitive polymer.
•
Process to fabricate a certain
structure :
- First a resist is spin-coated or
sprayed onto the wafer.
- A mask is then placed above the
resist.
- A radiation is transmitted through
the "clear" parts of the mask.
- The structure pattern of opaque
material (mask material) blocks
some of the radiation.
- The radiation is used to change
the solubility of the resist in a
known solvent.
Spin Casting : A Method Used For Resist Layer Formation
Optical Exposure
Highlights of a Typical
Lithography Process
- Using teflon tweezers, place the wafer on the wafer
chuck in the center of the Photoresist Spinner.
- Press the spin button which will cause the wafer to
spin at ~ 5000 rpm. Centrifugal force will cause excess
primer to move away from the center until all wafer is
primed and ready to accept resist. Then release spin
button.
- Give the resist a soft-bake in an oven at temperatures
between 90 and 120 °C to semi-harden the resist. Meanwhile
setup the mask aligner.
- For each layer there is a separate mask (patterned glass).
- Place the mask in the wafer holder so that the emulsion side
of the mask is facing downward toward the wafer.
- Carefully place the wafer on the wafer chuck of the aligner.
- Carefully slide the wafer chuck into the aligner so that the
wafer is positioned under the mask.
- Press expose button. A very bright light will come on inside
the aligner. The exposure time is set according to the type of
resist (~10 s)
- Immerse the wafer in the developer for the recommended
time ( ~ 30 s).
- Immediately after plunge the wafer into the beaker filled
with water to stop the development process.
ETCHING
• "Wet etching" is predominantly isotropic.
• However "dry etching" results in anisotropic or
vertical etch.
Dry Etching
(1) Vacuum enclosure ; (2) At least two electrically
separated electrodes ; (3) Provision for continuous
introduction of etching gas ; (4) A port for pumping ; (5)
A source of rf coupled to the electrodes to create plasma.
Highlights of a Typical Dry
Etching Process
- Prepare chamber.
- Load wafers.
-Plasma etch.
- Remove wafers.
Pattern Transfer
Gripper
Micromotors