Hello Alexandre

Using XeF2 to etch your silicon would be the perfect solution to you problem.
Exactly how to do it will depend on the type of silicon nitride you are using
and how much attack you can tolerate.  Please feel free to contact me if you
have any questions or want to try it.

Sorry if this is a duplicate but I tried to respond once before and it did not
seem to show up.

Regards
David Springer
XACTIX, Inc.
2403 Sidney St.
Suite 300
Pittsburgh, PA 15203
Tel: 412 381 3195
Mobile: 412 381 1136


Alexandre wrote:

Dear all,

We would  like to etch silicon (top layer of SOI wafers) using dry (or
wet) etch. We would like to get a good selectivity of this etching
solution with LPCVD silicon nitride (and PECVD silicon dioxyde, but less
important).

Up to now, we are using SF6 plasma. Si3N4 beams are defined on the top
Si layer. When the top silicon layer is etched, the SiO2 is an etch stop
layer and then the RIE etches underneath the silicon under the beams and
then releases them.

Any idea or suggestion for an etching solution (we prefer dry etch to
avoid a CPD step).

Thanks,

Alexandre