Hi Aaron. The only potential cause that comes to mind in this case would be some residue from the stripping process. Perhaps some areas are masked a little and so protected to an extent while others are more exposed and form the craters. This is not normal behavior for KOH solutions--they should etch nicely along the crystal plane. Incidentally, we do offer KOH solutions if you want pre-made product. I do not think your results would be any different, but if you determine the cause we can help you with the chemistry. Regards, Christopher Christuk Transene -----Original Message----- From: mems-talk-bounces+sales=transene.com@memsnet.org [mailto:mems-talk- bounces+sales=transene.com@memsnet.org] On Behalf Of Aaron Glatzer Sent: Wednesday, July 02, 2014 1:42 PM To: mems-talk@memsnet.org Subject: [mems-talk] KOH etch surface "craters" We are etching some 300 micron deep trenches using KOH, and we are occasionally getting "craters" in the trench bottom surface. These are 2-4 micron deep 50-75 micron wide spots on the bottom of the trench. Is this typical for KOH etch? Has anyone else seen this kind of thing? Any idea what causes it? Technical details: <100> silicon. Masked with 2kA low stress LPCVD nitride. Nitride etched with SF6 plasma RIE; we guesstimate we etch 2000A into the Si (based on known-etchrate, and observed overetch time on endpoint signal). Resist stripped in O2-ash/piranha/O2-ash sequence. KOH 45%, etched at 85C, for about 5.5 hours. Typically we get a mildly textured surface (per optical inspection), but as indicated above occasionally we get what look in microscope like blisters, but optical profilometer indicates is actually a "crater". Any insight into this is appreciated. thank you, Aaron G. -- Aaron Glatzer phone (419) 241-6963 x13 Lead Process Engineer fax (419) 241-6966 Midwest Microdevices, LLC aglatzer@midwestmicrodevices.com 329 14th Street Toledo, OH 43604 --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _______________________________________________ Hosted by the MEMS and Nanotechnology Exchange, the country's leading provider of MEMS and Nanotechnology design and fabrication services. Visit us at http://www.mems-exchange.org Want to advertise to this community? See http://www.memsnet.org To unsubscribe: http://mail.mems-exchange.org/mailman/listinfo/mems-talk _______________________________________________ Hosted by the MEMS and Nanotechnology Exchange, the country's leading provider of MEMS and Nanotechnology design and fabrication services. Visit us at http://www.mems-exchange.org Want to advertise to this community? See http://www.memsnet.org To unsubscribe: http://mail.mems-exchange.org/mailman/listinfo/mems-talk