How much is the tolerance of the angle? If the angle requirement is not strict, the simplest way is KOH etch. The etch rate can be 1-2um per minute. Good luck, Hongjun Zeng, PhD MEMS/Nano Scientist Microfabrication Application Laboratory University of Illinois at Chicago -----Original Message----- From: ning Subject: [mems-talk] How to etch Silicon into oblique walls using ICP? Hi everyone, Common goals of using ICP etching is to form vertical walls. But what I need to do is just the opposite. We want to etch in Silicon wafer some deep trenches with an oblique angle about 45 degree. And we want the etch rate to be as fast as possible. I am completely new to this topic, I really need some advice. Thanks. Ning