This cratering is not exclusive to KOH etch chemistries - I observed the same defects when etching ~500um deep square wells with TMAH. I have also observed them on commercial AFM cantilever chips. I never conclusively determined the cause, but I strongly suspect the cratering is due to a crystallographic defect in the silicon - either dislocation cores or voids that form from aggregation of point vacancies. There is an activation energy for vacancy formation and their equilibrium concentration is therefore temperature-dependent. During cooling from a high-temperature annealing or oxidation process the vacancies generally don't escape to a free surface, so they aggregate and form voids; these voids can also form during ingot cooling in the Czochralski process. I hope this helps. Best regards, Brian Stahl, Ph.D. Apeel Sciences On Thu, Jul 3, 2014 at 4:41 AM, Saleswrote: > 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 > _______________________________________________ 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