we used to get some roughness, but not to 2-4um levels used high quaility
SOI wafer though), could be defects in silicon, i have some JMEMS papers in
2003 and 2004 on optical actuators, check the KOH etching part, etched 80um
deep, i think 10% KOH, 6um/hr slow etch.
how deep are you etching? what is your etch rate?
slower etches are better in general. I also used SOI which is very
expensive and high quality wafers, so that could be an issue,
you are probably etching into bulk silicon right? may be try to get better
silicon less defects etc,

-M


Mehmet R. Dokmeci, PhD

Instructor in Medicine, Harvard Medical School

65 Landsdowne St., PRB 252, Cambridge, MA 02139

email: [email protected]


On Wed, Jul 2, 2014 at 1:41 PM, Aaron Glatzer <
[email protected]> wrote:

> 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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