The wrinkling you're seeing in the silicon nitride
is most likely stress. If you're depositing a 4000A
thick stoichiometric LPCVD nitride you will definitely
have a compressive stress 300MPa and up, 4000A is on
the thicker side as well. I believe Berkeley should
have a recipe for tensile low stress LPCVD SiN, which
is typically silicon rich and deposited with higher
DCS to NH3 ratio than stoichiometric nitride. I've
seen ratios ranging from 4:1 to 6:1 in literature.
Its also possible to get low stress SiN using PECVD,
but these films are less durable, they usually have
many more pinholes allowing KOH leakage, and have a
much higher etch rate in HF solutions than their LPCVD
counterparts, however if this is not a problem, they
are probably easier to deposit than LPCVD films.
good luck.

dave kharas Ph.D.
Sarcon @Sarnoff Corp.



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