Tentative clear of shutdown ... but use with extreme caution!!!

John Shott shott at stanford.edu
Fri Sep 11 23:58:39 PDT 2009

SNF Lab Members:

I have just cleared the shutdown on drytek2 .... but want to make sure 
that you all read this very carefully before proceeding with any 
critical etching.

As you know, this machine has been experiencing pump down and vacuum 
readout problems.  We have now replaced the main vacuum pump as well as 
the Capacitance Manometer with a brand new 1 Torr head. The other 
dryteks (1 and 4) use a 10 Torr head.
This difference is why I am asking you to proceed with caution in any 
etching that you do with drytek2 this weekend.  While I believe that we 
are reading and controlling to a proper pressure .... that is, when it 
reads 150.0 it is actually 150 mTorr, there is a chance that that is not 

Why the confusion?  The 10 Torr heads on dryteks 1 and 4 produce a 0-10 
V output signal when the chamber pressure varies from 0 - 10 Torr ... so 
that a 150 mTorr vacuum should produce 0.150 V.  The 1 Torr head on 
drytek2, however, produces 0 - 10 V output as the pressure varies from 
0-1 torr ....so that 150 mTorr vacuum produces 1.50 V.  I believe that I 
have properly set the pressure controller on drytek2 to accommodate this 
10X more sensitive capacitance monitor.

In any event, I THINK that everything is set up properly .... but we 
have not had time to yet run test wafers or make corroborating pressure 
measurements.  As a result, if you have a critical etch for drytek2, I 
strongly suggest that you wait until Elmer and Nancy can perform 
additional machine tests and run test wafers, respectively, to make sure 
that I am not in error.  If, on the other hand, you have a non-critical 
usage, such as a descum, you may be willing to run some wafers this 
weekend,  I'd still recommend running test wafers just to be sure .... 
but I know that there may be some pent up demand for this tool, so I 
wanted to clear the shutdown so that you could use it .... but also warn 
you that while I believe we are controlling pressure correctly, that we 
may still have a pressure readout problem.

Thanks for your continued support,


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