Hi James I suspect you hace a compressive device layer and tensile nitride once the nitride is gone, the device will buckle / warp shay Original Message: ----------------- From: J.H.T. Ransley jhtr2@cam.ac.uk Date: 30 Jan 2006 17:43:24 +0000 To: mems-talk@memsnet.org Subject: [mems-talk] Stress in Si films after RIE Dear all, I am trying to develop a MEMs process using SOI wafers. I am making membranes successfully using a TMAH wet etch but am having problems stripping the protective SiNx coating from the device layer once the membrane is fabricated. Once the membranes are fabricated I remove the Buried Oxide completely with a wet etch - at this point the membranes appear unstressed (looking at them by eye). I then use a dry CF4 plasma etch to remove the nitride - this will obviously etch the Si too - I try to time this etch carefully but there is always some etching of the Si underneath. After this step the membranes appear to be significantly stressed. Is this expected? I can't see how the dry etch could introduce stress in the membrane but I am ready to be corrected if anyone else knows otherwise... Is this problem likely to be solved by using a wet etch (hot phosphoric acid) or do I need to look for an alternative cause for the stress? Any help will be much appreciated. James Ransley