STS2 -- Found Matching Network Cooling Problem

Jim McVittie mcvittie at cis.Stanford.EDU
Tue Jul 13 17:10:56 PDT 2010


Hi,

1.	Coil Phase/Magnitude detector tuning

Because of all the matching problems we have had with STS2, I took out the
phase/magnitude detector and retuned it using a 50 ohm dummy load, the rf
generator and an oscilloscope. The phase/mag detector is the sensor used
by the matching network controller to auto match the plasma impedance to
50 ohms. I found it was quite a bit off.  On putting the detector back
into the system, I find that we can get significantly lower reflected
power for the switched processes. However, the unswitched processes (O2
clean) now have a higher reflected power.  I am also seeing heating
effects in that the matching getting worst as I use the system.  It seems
that the phase/mag detector is warming with use.

2.  Matching Network Box Heating Problem 

I think I have found the root problem for our matching problems. In
checking why the detector is showing signs of heating, I found that the
cooling fans on the box containing the coil matching network and the
phase/mag detector were mount wrong. Both fans were blowing inward with no
clear pathways for the air to get out. This explains why it has taken so
long for the rf system to recover after heating from rf power drop outs
from poor matching. I have reversed one of the fan.  I am now wondering rf
detector diodes in the detector may have been over heated and are part of
our problem. Lets see how the improved cooling is working. If we are still
matching seeing problems, I will replace the diodes.

	Jim 

-- 
--------------------------------------------------------------
James (Jim) P. McVittie, Ph.D.	        Sr. Research Scientist 
Paul G. Allen Building                  Electrical Engineering
Stanford Nanofabrication Facility       jmcvittie at stanford.edu
Stanford University             	Office: (650) 725-3640
Rm. 336X, 330 Serra Mall		Lab: (650) 721-6834
Stanford, CA 94305-4075			Fax: (650) 723-4659 





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