STS2 -- Found Matching Network Cooling Problem

Jim McVittie mcvittie at cis.Stanford.EDU
Tue Jul 13 19:18:06 PDT 2010


I was wrong about the cooling. Changing the fan made no difference and
there is an air pathway around the rf feed to the coil out of the matching


On Tue, 13 Jul 2010, Jim McVittie wrote:

> 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 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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