| 3.4 Surface Micromachining
Surface micromachining involves processing above the substrate, mainly using it as a
foundation layer on which to build. It was initiated in the 1980’s and is the newest MEMS
production technology. Material is added to the substrate in the form of layers of thin films
on the surface of the substrate (typically a silicon wafer). These layers can either by structural
layers or act as spacers, later to be removed, when they are known as sacrificial layers. Hence
the process usually involves films of two different materials: a structural material out of
which the free standing structure is made (generally polycrystalline silicon or polysilicon,
silicon nitride and aluminium) and a sacrificial material, deposited wherever either an open
area or a free standing mechanical structure is required (usually an oxide).
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