TABLE OF CONTENTS A good understanding of the physical properties of materials and the ways in which materials can be grown is an integral part of designing and fabricating a microsystem, and being able to predict how it will behave. Although a range of novel materials are being developed for microsystems applications, such as diamond-like carbon, gallium arsenide and low temperature polymers or resins (most notably SU8 and polyimide) the traditional CMOS materials silicon, silicon dioxide, silicon nitride and a range of metals still dominate. They are likely to continue to do so for the foreseeable future, because the foundry processes for these materials are well developed.
Crystalline silicon wafers form the backbone of most MEMS devices, allowing integration of CMOS devices with the microsystem on the same substrate. The wafers themselves are usually produced from purified molten silicon by introducing a small crystalline silicon seed into the melt. In what is known as the Czochralski process, the silicon seed is rotated with respect to the melt, and slowly withdrawn from the solution. Silicon atoms solidify on the seed in the same crystal orientation as the seed, to produce a large ingot of single crystal silicon. This ingot is then cut, polished and lapped to produce the silicon wafers that we are familiar with, and upon which devices can be built.
This section looks at how to produce other materials on the surface of the silicon wafer. In the case...
