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  m.

Measurement and Information System N/MEMS System

N/MEMS AND/OR IC PROCESSES

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. 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 SiO 2 dielectricsPoly-Simetals Deposited SiO 2 Deposited Si 3 N 4

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 ( ~ 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. LITHOGRAPHY

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