N ano/ ano/ Micro Micro Electro- Electro- Mechanical Systems Mechanical Systems (N/MEMS) (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.
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Nano/Micro Electro-Mechanical Systems (N/MEMS) Osama O. Awadelkarim Jefferson Science Fellow and Science Advisor U. S. Department of State & Professor.
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Nano/ano/MicroMicro Electro-Mechanical Electro-Mechanical Systems Systems (N/MEMS)(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.
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.
MATERIAL FOR N/MEMS AND/OR ICs
• 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:
ELECTRONIC MATERIALS
Thin films
thermal SiO2 dielectrics Poly-Si metals
Deposited SiO2 Deposited Si3N4
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.
- 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 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.