System update ....

John Shott shott at stanford.edu
Thu Jul 3 17:16:27 PDT 2008


SNF Pquest Fans:

Here is an update of what we have (and have not) done on the PlasmaQuest:

Today, Elmer and Mike did a full chamber clean and wipe down.  At the 
same time, they shut off the turbo to pull out the gate valve.  They 
removed quite a collection of broken wafers and fragments from the gate 
valve and the screen on top of the turbo valve.  At the same time the 
main O-ring seal of the gate valve was replaced.  To test that the gate 
valve is now closing fully, the system was put in a state where the main 
gatevalve was shut but the chamber and the loadlock were at atmosphere.  
If the gate valve were leaking, the turbo would have been at a high 
pressure and the load lock lid would have been unable to be manually 
lifted.  As a result of this test, we believe that the gate valve is 
closing fully.

After the wet clean, the chamber was cleaned with an oxygen recipe for 
6000 seconds.  Any folks doing any etching will likely want to make sure 
that they have seasoned the chamber properly to meet their needs and to 
check etch properties carefully.

What has not yet been done:

The ferrofluidic rotary seal that controls the wafer up/down clamping 
motion is showing some (but not yet severe) leakage.  When I was 
observing system pressure with the gate valve shut, the rate of rise was 
higher when the clamp was either going up or down than it was when the 
clamp was either fully open or fully closed .... that is, the rotary 
feed through seems to leak more when it is in motion that when it is not 
in motion. This is fortunate because the rotary feedthrough is not in 
motion during etching .... only when the wafer is being loaded or 
unloaded. Unfortunately, this is not an easy part to acquire.  It 
currently has a 4 week lead time from Nexx and one of the 2 
manufacturers of the feedthrough can do no better.  While I am still 
trying to contact the other manufacturer, we may have to wait on this.  
Hopefully, this seal will hold on during that time and allow useful work 
to be done as it does not appear to be a severe leak at the moment.

The other part on which we are waiting is the special "soft and squishy" 
(AKA Shore A durometer 40) O-ring that is used for the backside helium 
seal.  We expect those to be delivered early next week.  At this point, 
we believe that helium backside leakage with the existing O-ring is 
within tolerable limits.

Let me know if you have any questions and I'll try to do my best to 
answer.  If there are process questions, of course, either Jim Kruger or 
Jim McVittie are your best local sources of information.

Happy processing,

John







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