Marie-

I would say your best bet is to dry etch using a high pressure SF6 process
in a dry etcher. Of course the actual process conditions will depend on how
deep you want to go, how quickly you want to get there, and how much
undercut is necessary. There are other fluorinated gases that will do this
as well, if you do not have SF6 or do not wish to use it.

Michael Marrs
Process Engineer
Trion Technology
+1 (480) 968-8818 ext. 25
[email protected]