Stress in nitride films is an interesting, and sometimes maddening topic.
Stress in a stoichiometric film (i.e. Si3N4) is very high, typically 1 GPa
tensile. Because of this huge stress, film thicknesses are limited: wafers
will break or be severely warped if the thickness is to large.

Usually non-stoichiometric films are deposited to combat this issue. These
films are silicon-rich -- closer to Si4N4 than stoichiometric Si3N4. Film
stress tend to be in the range of 10-100 MPa. Depending on your application,
you have a couple of options, LPCVD or PECVD. LPCVD films will tend to be
pinhole free and are (generally) more resistant to wet chemical attack.
However LPCVD films also tend to be non-uniform, with thickness and stress
variations from the edge of the wafer to the center of the wafer and also
from the top of the boat to the bottom of the boat.

PECVD films are more uniform (I think). Historically, PECVD nitride wasn't
suitable for a KOH etch mask, because of excessive pinholes.

Bill Eaton, Ph.D.
Materials & Analysis Manager
NP Photonics
mailto://[email protected]
www.parvenutech.com

> -----Original Message-----
>
> I really appreciate if you could help me find data on
> residual stresses
> left in Silicon Nitride layers on usual and hi-quality
> wafers. For our
> research, we would need to find very-low-stress
> nitride-layered wafers or
> methods to create them by our own. Prices, availability and
> literature are
> welcome.
>

http://mail.mems-exchange.org/mailman/listinfo/mems-talk
Hosted by the MEMS Exchange, providers of MEMS processing services.
Visit us at http://www.memsnet.org/