Alexander,

vapor HF etching is indeed a straightforward way to release SOI
structures without sticking. In our lab at ETH Zurich, we currently
work with a commercial, laboratory-type HF vapor etcher from AMMT in
Germany (www.ammt.de). In this case the wafer is heated to avoid
HF+H2O condensation on the surface, therefor no sticking has been
observed. Etching takes an hour or two depending on the structures
(typical rates for buried oxide are between 5 and 10 um/hr).

Best regards,

Jan
------------------
Dr. Jan Lichtenberg
Teamleader Microfluidics and Biosensors
Swiss Federal Institute of Technology (ETH) Zurich, Switzerland

Sunday, October 24, 2004, 6:49:54 PM, you wrote:

OAE> Hi there,

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

OAE> Thanks a lot,
OAE> Alexander