Problem drytek4 2003-01-17 11:10:39: drytek4 nitride etching

sabnis at sabnis at
Fri Jan 17 11:10:41 PST 2003

Last night I used the drytek4 to etch SiN off of
my wafers.  
Recipe:  100 sccm SF6, 150 mTorr, - 30 V bias (~120 W),
etch rate 2000-2500 A/min.
This recipe has been rock solid since about last April
or May (after Len did major repairs on the machine).
In the week just before the lab holiday shutdown, I believe
the showerhead and chamber were wiped down to
remove the built up polymer, etc.  I used the machine
after it was cleaned that week and noticed that my bias 
and etch rate had dropped to one half their usual values.  
Fortuntaely I was able to get my samples etched.
Last night I used the machine for the first time this month
and got terrible results.  The etch rate was very inconsistent
and the uniformity over the wafer was terrible - in some 
places etching occurred and in other places 
there was no etching.  I believe that something has changed
since the cleaning in December.   
Could someone please take a look at the machine ?
I can provide SiN test samples.
Other minor point - we need more logsheets - the notebook
is full.   
- vijit sabnis

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