MEMS Fabrication�

Micro-Electronic Mechanical Systems

By

Andy Lingley, Matt Leone, Brad Pierson

&

Faculty Advisor Todd Kaiser

Project Goals:

� To obtain multiple working MEMS devices on a single wafer, and to quantify their results

� Build a lab manual capable of walking undergraduates through the process in a fifteen week laboratory

Scope:

����� Accelerometers and pressure sensors were chosen as the MEMS devices.� It was imperative to understand the devices before the process steps were developed.� The picture seen here gives a great illustration of the accelerometer design.� A simple cantilever beam will flex as a force or acceleration is applied to the proof mass.� Using the piezoresistive affects of silicon a change of voltage can be measured as the silicon is deformed.� The piezoresistive affect is a change of resistance due to a change in crystalline shape on the microscopic level.

Many devices can be made utilizing these peizoresistors.� In our case we also designed a few pressure sensors and a tactile sensor.� By simply fixing four sides of a square and deforming the middle, a strain will be created at all fixed points.� This is similar to the fixed end of the cantilever.� Below are two simulations of actual designed devices. This simulation was run prior to completion of the mask design.�

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The Process:

��������� The fabrication process can be broken up into five simple steps.� Below is a flow chart of these steps followed by a short description of what each step should accomplish.� Clicking on the flow chart will take you to a link with the all steps required to build an accelerometer.

Note:� Each Step has a link discussing step specifics to our Accelerator and Pressure Sensor Design.

~Mask Design:�

��������� Mask design is crucial to success in all microfabrication.� All masks must be able to be aligned and all measurements must be precise, taking into account etch planes and doping times.

~Film Deposition:

��������� By growing a small layer of glass on a silicon wafer, it can serve as an insulator for future steps in the process. This glass can be grown on silicon by simply exposing it to oxygen under high temperature (1000 C) growing SiO₂.�

~Photo Lithography:

��������� A thin layer of photoresist will be applied on to the SiO₂, then this photo resist will be patterned with a mask and exposed to UV light.� This UV light breaks down the exposed resist leaving the desired pattern after development.

~Etching:

��������� With a pattern of exposed silicon on the wafer, etching cuts the desired shapes into the wafer.� The crystalline planes of silicon will cause this etching to be done at some angle.� In our case, a chemical called Tetramethyl Ammonium Hydroxide (TMAH) will be used, resulting in an etch angle of 57.4 degrees.

~Doping:

��������� This step is done instead of etching if different electric properties are required.� By choosing the proper chemical, electrons and/or holes can be made in order to fit specifications.� This is often done in order to create resistors on a wafer.

�And now let�s meet the Team:

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	Matt Leone
Andy Lingley
		Brad Pierson

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Faculty Advisor Todd Kaiser

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Page made in support of EE 492 and also the continuing research in the Montana Micro-Fabrication Facility, optimizing discussed topics, and furthering understanding of all process steps.