"unique" situation!

Harshal Surangalikar s_harshal at yahoo.com
Thu Jun 30 12:20:04 PDT 2005


Hello All,

I have a unique situation with my wafers that I wanted
to share to see if anyone has had a similar/close
experience and any ideas/ suggestions about the same.

i am processing double-side polished wafers to put a
stack of nitride-PSG-nitride  films. the steps were as
follows:

- wbdiff clean
- NEWLSN nitride dep for 2.25 hrs (target thickness ~
1um)
-wbdiff clean
- PSG400 for 1.25 hrs (SiH4=22, PH3= 86,target
thickness ~ 2.1 um)
- inert anneal, 1000AN, 2hrs.

After the anneal step, one side (back side in BPSG
furnace) in all the wafers shows a damaged and whitish
 residue-like appearance for the PSG layer that is not
seen on the front side, the front sides show normal
PSG color. I am not sure why the discoloration should
occur only on the back side except for the reason that
the back sides were facing inside in the bpsg furnace
and may have had less deposition than the front side. 

any ideas?

many thanks for your time and help,
harshal.





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