Hi,

I need to isotropically etch ~200 nm into a saphirre wafer to suspend a
small gold wire. Unfortunately I don't have access to an ICP RIE, and
H2SO4 with H3PO at 300 plus degrees is not an option. The etch does'nt
need to be fast, it can take a couple of hours if necessary. I tried
HF,BHF and NH4OH at 80 degrees, but so far the only etching is into the
niobium metallization ( which will be masked on the final wafer ). Does
anyone have any suggestions?

Thanks for your help,

Gabe