I've been using 1200 Angstroms of Cr as a mask for etching Pyrex to a depth of
5 microns with BOE. (Photoresist wouldn't adhere well to the Pyrex).  The Cr
seems to hold up fine during this 3 hour etch.  However the BOE undercuts the
Cr ~16 microns for a 5 micron etch depth.  I don't know if this is due to poor
adhesion of the Cr or something else.

If you can tolerate this sort of undercut, perhaps a thicker Cr layer will
solve your problem.

I recently tried etching the Pyrex by SF6/O2 RIE which reduced the 5 micron
etch time to 1 hour, with ~1 micron of undercut.

Roger Shile

>>> majumdar@uiuc.edu 03/01/02 12:40PM >>>
Hi,
        Right now we're using chrome-gold-chrome layers, 100A-150A-100A to
protect for glass etching. I noticed that if I do a BOE etch over 35
minutes, it starts to eat through the layers some and makes the channel
edges rough. I wondered if, in addition to thicker protective layers, the
preparation of the glass surface had an effect, say a SC-1/BHF clean
instead of H202:H2SO4.

THanks,

Ziggy
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