Hello, everyone:

There are always some black spots on the surface of PECVD SIN, the ratio we used
is SiH4:NH3=4:1, this ratio seems no problem before.  Black spots began to
appear since the equipment leaked gas, but after we solved the problem with gas
leakage, the spot still exists.
Has this situation ever happen to anyone before?  What are the possible reasons
for it?
I'll appreciate it very much for your help. Thank you for your time very much!

Best wishes!
Yours sincerely,
Harriet