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.






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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

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