Nimo:

I have seen this effect on wafers that have been processed thru a boron
nitride operation and somehow form a silicide in certain areas of the device
wafers. Otherwise you might have a form of polymer from the drie etch left
behind. An oxygen process at the end of your etch process or ending on an
SF6 period should remove those polymers. Also, using a few drops of
surfactant in your BOE might help to wet the surface being etched and allow
a more complete removal of the oxide.

Bob Henderson

-----Original Message-----
From: mems-talk-bounces+bob.henderson=etchedintimeinc.com@memsnet.org
[mailto:mems-talk-bounces+bob.henderson=etchedintimeinc.com@memsnet.org] On
Behalf Of Elina Kasman
Sent: Wednesday, July 21, 2010 9:19 AM
To: mems-talk@memsnet.org
Subject: Some silicon-dioxide will not etch in BHF...can that be?

It is possible that you had an effect of material diffusion or re-deposition
during the DRIE process, which would make the oxide more resistant to BHF.

Elina