I always etch two silicon wafers or chips sticked to each other, from front
sides using some black-wax. This process both protects front sides and let
you etch two wafers at the same time. Also one wafer can be handle if you
want. I succeeded to fabricate two 4 um thick diaphragms at the same time
with this process.

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Isa Kiyat

Bilkent University
Department of Physics
06800
Ankara, Turkey