Dear Kevin:

I suggest that you try not to use PECVD in this case or if you use it make sure
that it is densified, thick, and as close to stochiometric as possible.

PECVD nitride is not a good etch mask for KOH. However, LPCVD which is a good
one would probably ruin you Aluminum layer because of its high temp of
deposition. If you must use PECVD, try to measure the etch rate in the KOH
solution, and also try to use process parameters that can assist you in
densifying it. We can help you with the determination of process parameters
using MEMaterial software.

Sincerely,

Fariborz Maseeh.