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: [email protected] [mailto:mems-talk-
[email protected]] On Behalf Of Aaron Glatzer
Sent: Wednesday, July 02, 2014 1:42 PM
To: [email protected]
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 [email protected]
329 14th Street
Toledo, OH 43604
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