Hi,
  I've been trying to use a 2 micron thick LPCVD silicon nitride layer
(from the Berkley Fab) for release to produce a suspended membrane over
an area of 7mm x 7 mm. The wafers are (100) and the only layer on them
is the silicon nitride. That is, there is no oxide between the wafer and
nitride.
  Techniques I've tried for release:
   DRIE
     Samples are diced and adhered to a handle wafer. The nitride is the
stop layer. Incidentally, the nitride works as a great stop layer
contrary to what STS claims. The adhesives between die and handle I've
tried are super glue, resist, thermal grease, and more. No mater what
I've tried the samples are fractured when they come out of the DRIE.
   DRIE+KOH
     In this approach I DRIE until I'm about to reach the nitride (about
10-20 microns of silicon left) then I put the die into KOH. I've tried
this with 200 rpm stirring, no stirring and very small solution volumes
to reduce convection all to no avail!

  I'm begining to think there is too much tension although I think these
exact films were used to make X-ray masks that were released to form
membranes as large a 1 cmm in diameter. Is there some technique to
introduce compressive stress in the film to compensate?

Any input is welcome,
  Mike Martin
  U of Louisville Fab.