Some of my students have recently been working with a relatively unknown
silicon etchant, xenon difluoride (XeF_2), which has some remarkable
properties. It is a white solid which sublimates at room temperature, yielding
a vapor which will etch silicon isotropically at several microns per minute or
more. It is extremely selective to aluminum and silicon dioxide, and can be
masked with photoresist. We've been using it as a post-CMOS etch in place of
EDP or TMAH.

There's lots of literature on this stuff, but nothing that we've found that
addresses much that's "MEMS relevent". We're working to characterize etch rate
vs. pressure, silicon doping (it eats N+ faster than anything else), and
selectivity to different materials, which brings me to the point of the email:

Anyone who would like to try it out is welcome to send us a sample, or come use
the system themselves. If you've got an unusual material, or a silicon etch
problem that the standard anisotropic etchants can't handle, send us some mail.

ksjp
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Kristofer S.J. Pister                                      (310) 206-4420
UCLA Electrical Engineering                            fax (310) 206-8495
405 Hilgard Ave.                             email: [email protected]
Los Angeles, CA 90024-1594               ftp, http: synergy.icsl.ucla.edu