Andrea, I've found that the biggest challenge when using evaporated metal this way is particles. Every particle results in a pinhole in your mask that allows the etchant to get under the mask. Dan -----Original Message----- From: mems-talk-bounces+dan.ruiz=honeywell.com@memsnet.org [mailto:mems-talk-bounces+dan.ruiz=honeywell.com@memsnet.org] On Behalf Of Andrea Mazzolari Sent: Friday, April 02, 2010 10:41 AM To: mems-talk@memsnet.org Subject: [mems-talk] metallic mask Hi all, i need to thermal evaporate a metallic mask on a polished silicon wafer. The mask should withstand 40% KOH etch for 5 hours. I tried 20/30 Cr/Au, but it seams that it is not working: after about 1 hour etch many pinholes are generated in the Cr/Au layer, KOH penetrates such pinholes and etch silicon. Any suggestion on how to improve the resistance of Cr/Au layer ? Any alternative to Cr/Au ? Thanks, Andrea