Plasma quest update ....

John Shott shott at
Thu Aug 7 19:10:10 PDT 2008

Plasma Quest Community:

Elmer did some more fine tuning of the clamp assembly today and it is 
behaving pretty well.   In particular, he did 2 key things:
1. He discovered and adjusted the "holding wedge" underneath the up/down 
mechanism at the left of the chamber.  Proper adjustment of this seems 
to prevent the clamp from sliding to the left under higher clamping loads.
2. He also recuced the clamping force by reducing the spring preload at 
each corner of the clamp assembly by loosening the allen scred by 2 1/2 
turns on each corner.

Testing under Jim Kruger's oxygen3 program showed a helium "blow by" of 
roughly 4.0-5.5 sccm to maintain the 10 Torr backside pressure and 600 
watts of power (I think) resulted in a backside bias of about 67-68 volts.

At this point we are releasing it again for cautious use subject to the 
following conditions:

1. Because this is the full-clamp ring rather than the "finger style" 
clamp ring, anyone needing to etch close to the ring should check etch 
rates carefully ... this clamp will likely affect etch characteristics 

2. Please be observant when loading and unloading to be on the lookout 
for any problems.

3. Please check your etch rates carefully before committing critical 

4. Remember that we are in fluorine chemistry mode for a few more days.

If you get good results, please say thank you to Elmer, Cesar, and to 
Jim Kruger ..... they've each made important contributions and been 
quite diligent in resolving these issues.  If you encounter problems 
.... send them to me.

Best of luck,


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