SangHwui,

I have been using a sputtered Cr/Au layer on my pyrex wafers as an
etch mask.  500 Ang Cr, 5000 Ang Au.  This can be patterned with
photolithography and Cr/Au wet etching.  Then strip the resist and go
into your pyrex etchant.  This stands up much better to HF than the
resist, but there is some undercut.  For your purposes, undercut might
not be a bad thing, since it will give a "slope" on the edge of your
etched region.  With long etches I observe significant roughening
of the pyrex surface, but I am etching much deeper (80 microns deep in
concentrated (49%) HF) than you are, so it might not be so bad for
you.

That's my experience.  If anyone has suggestions for how I might
reduce roughening or undercut in my pyrex etch process I would
appreciate the input.

Rob
--
Robert D. White
Graduate Student Research Assistant
Vibrations and Acoustics Lab, 2200 EECS
Mechanical Engineering
University of Michigan
Ann Arbor, MI 48109

(734)936-3824
[email protected]