Page 420 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

400 MEMS-IDT MICROSENSORS

Figure 143 Basic steps in the fabrication of the seismic mass

Process Flow of Seismic Mass:
The steps involved in the fabrication of the seismic mass are outlined here and involve
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the sacrificial etching of silicon dioxide (see Figure 14.3) .
1. A sacrificial oxide is thermally grown on the silicon wafer.

2. A polysilicon (structural layer) is then deposited by low-pressure chemical vapour
deposition (LPCVD) on the sacrificial layer. Polysilicon has good structural properties
and is commonly used. This structural layer is thick enough (1 um) to support itself.
The polysilicon is patterned and etched using ethylenediamine pyrocatechol (EDP).

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Full details of lithography and etching techniques are described in earlier chapters.