Running Jim Oxide:
dummy 120sec, DC bias good
test wafer 120sec, noticed DC bias low at the end of the run
measured etch rate: 589A/min (typically between 3300-3500 A/min)
ran test wafer again, watching DC bias. It remained near -500V for the entire 120sec etch. Measure etch rate of 3473 A/min.
Ran two more test wafers for 120sec, DC bias remained steady around -500V.
Loaded 6 production wafers for 144sec. First one ran smoothely. Second one started smoothely, about 50sec into the run DC bias dropped. I stopped the run at 60sec in an aborted the rest.
This problem happened a while back and it turned out to be the quartz ring was shorting.
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