There is an adhesion promoter for Parylene - check with manufacturer. It
will help with adhesion of the film to the wafer. The film also has to
be relatively thin ( <2um) and you've got to have a way to remove it
after the etch. Coating over film of SiO2 sounds like a good idea.

Parylene does tend to delaminate during long etch cycles.

-----Original Message-----
From: Dirk.DeBruyker@parc.com [mailto:Dirk.DeBruyker@parc.com]
Sent: Wednesday, October 08, 2008 11:55 AM
To: mems-talk@memsnet.org
Subject: Re: [mems-talk] Parylene mask for KOH etch

I tried this. You should do some silane chemistry on the SiO2 surface to
promote parylene adhesion (see e.g.
http://engineering.tufts.edu/microfab/index_files/docs/Parylene.pdf).
Even then, it doesn't work too well, the parylene tended to delaminate
during long etch cycles.