If this is just for small volume, research type device you can always do
vapor HF.  Pour a little 49% HF into a container and suspend the wafer or parts
just above the surface.  You may still get some sticking as the by product of
the etch is water.  This can be avoided by adding heat to the back side of wafer
(how you do this is up to you). While this isn't the most elegant solution it
can get you parts in a pinch.  Just be aware of the hazards of working with HF
and take appropriate safety precautions.

-Dave Marx

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Oudalov, A. (EL)
Sent: Sunday, October 24, 2004 9:50 AM
To: '[email protected]'
Subject: [mems-talk] Sticking of fragile MEMS structures


Hi there,

I am trying to release a comb drive structure etched by deep reactive ion
etching (DRIE) on a SOI silicon wafer. I try to make very thin gaps between
the comb drives to have a large electrostatic force. Since the spring
constant of my supporting structure is small I get problems when I release
the chips in buffered hydro-fluoric acid (BHF). The adjacent combs stick
permanently and the device is broken. I also tried critical point drying,
the yield is little higher but not satisfactory. Who knows about another,
more gentle method to release my combs?

Thanks a lot,
Alexander

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