Late night observations ....

John Shott shott at stanford.edu
Fri Apr 11 07:40:47 PDT 2008


Elmer et al:

A came back late last night to see the "middle of the night" problem and 
was rewarded by seeing it fail.

Mohammed Islam had just used the machine, successfully, from roughly 
10:45 to 11:30.  I took over and tried to run recipe 3.  The chamber had 
been open approximately 10-15 minutes.  As I began by run, the Hex and 
Hot LP were reading 31 and the Cold Lp was reading 21.

During rough pump, the Chamber TC reached 1 Torr after about 1.1 min and 
was at 216 mTorr by about 1.5 min.
When the Turbo came on the Hex was down to 23 and the Hot LP was at 32.

Following are the ion gauge readings:

1 min:   0.93
2 min:   0.85
2.5 min:   0.82
4 min:   0.76
5 min:   0.74
6 min:   0.73
somewhere here it "jumped" down by about 0.15 ...
7 min:   0.56
8 min:   0.56
10 min:   0.57
11 min:   0.58

A second run (without venting) showed no better performance and I gave 
it up at about 8 minutes into that run with it reading 0.57-0.58 mTorr.

So, what is going on:

1. Is it humidity or temperature in the cleanroom, due to the throttling 
back of the air flow?  I've asked Leonard for temerature and humidity 
traces for that portion of the lab for the last 48 hours.

2. Is the ion gauge "worn out"?  I certainly can't explain why this 
would be time dependent.

3. Is the heat loop capacity a bit marginal?  I notice that there is a 
slow leak on the back of the hot loop reservoir.  Is the level a bit 
low?  We should probably top it off, at the very least, and, when we 
have the time, address that slow leak.

4. Is the turbo marginal?  This is an old "oiled" bearing turbo isn't 
is?  Is the oil level and oil quality what it should be?

I'll send out further word once I have temperature and RH data from 
Leonard ...

Thanks,

John





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