Hello Aaron,

we often observed the "crater landscape" or "orange skin" while KOH and
especially TMAH etching. Following measures improved the surface quality
(high purity chemicals implied): annealing of potential crystal defects
before etching and scrupulous acid cleaning of all etching equipment. The
influence of light on the etching (depending on type and amount of dopants)
should be considered also.

Regards,
André

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Auftrag von Aaron Glatzer
Gesendet: Mittwoch, 2. Juli 2014 19:42
An: [email protected]
Betreff: [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.






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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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