Hi Harriet

How does the black spot look like?  Does it look like created by buring or
like a pin hole or sort of a cluster of dust?

If it looks like burning then it can be from plasma arching. But plasma
arching is rare in well tuned system. If it looks like brownish dust, it can
from the dirty chamber.

     Was your sample clean before loading into the PECVD chamber?

regards,

Samadhan
INESC-MN


----- Original Message -----
From: "xi liang" 
To: 
Sent: Wednesday, August 26, 2009 5:08 PM
Subject: [mems-talk] Black spot with PECVD SIN


> 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 wesolved 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