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