Since TMAH is an anisotropic etchant of silicon, for (110) plan wafer the etched walls will be perfectly vertical (the etch is much slower against (111) plane and this will result in vertical walls). However, this also means that your etch mask has to be alligned with the flat, otherwise the etch will "correct" itself and find the (111) plane even if it's not aligned with your mask. You will have some underetching, but these will also be vertical. 500um is one long etch. Elina Kasman Process Development Engineer, R&D Engis Corporation -----Original Message----- From: Andrea Mazzolari [mailto:info@alientech.it] Sent: Saturday, July 08, 2006 8:51 AM To: General MEMS discussion Subject: [mems-talk] Etch through Si wafer with TMAH Hi all. I need to etch through a (110) silicon wafer 500um thick. I'm planning to use TMAH. Will walls be perfectly vertical ? If not, which etchant could i use ? In case of tmah etch will under etch responsible for not vertical walls ? Based on what i know, walls will not be perfectly vertical, this sould be due to under etch... i'm i wrong ? Could someone suggest me some article on this argument ? Thanks! Andrea