>   Does anyone know whether it is possible to produce low
> stress nitride films that are a micron thick or thicker?

Low stress nitride coatings can be done by either LPCVD or PECVD. I think in
both cases the films are silicon rich, i.e. they're non-stoichiometric.
LPCVD low stress nitride is difficult to control: typically you'll see
thickness and stress variations from the top of the boat to the bottom of
the boat and edge-to-center variations within a wafer.

Thicknesses in excess of two microns are possible.

>   How thick of a silicon nitride film would be required to span 8mm
> after release?

Hmmm. You might be able to make some theoretical calculations on thickness,
but those will be based on how much tensile stress it would take to rupture
a diaphragm. In practice, the other forces acting on the diaphragm may be
much higher. You'll have to be very careful handling the wafers. 8 mm seems
somewhat ambitious, but if you're only making a few discrete devices, it
should be achievable.

Bill Eaton, Ph.D.
Materials & Analysis Manager
NP Photonics
5706 Corsa Avenue, Suite 100
Westlake Village, CA  91362
Voice:  (818) 991-7044 x211
eFax:   (503) 214-5559
mailto://bill@npphotonics.com
www.parvenutech.com