While running Jim Ox in chamber B I noticed the DC bias voltage drop suddenly and the corresponding etch rate was low. Here is what happened
wafer 1: dummy wafer, Jim Ox 120sec. Ran smoothely
wafer 2: test wafer with ~1.5um LTO oxide, Jim Ox. 120sec. Towards the end of the run I noticed the DC bias was close to 0. I measured the etch rate to be 589 A/min, much lower than typical ~3300A/min. There was nothing else to indicate a problem had occured.
wafer 2 (run 2): Same wafer and same process as previosly, ran smoothely with consistent DC bias around -500V. Etch rate measured 3473A/min
wafer 3&4: test wafers, ~1.5um LTO oxide, Jim Ox. 120sec. Both ran smoothely, consistent DC bias, good etch rate
wafer 5: production wafer, Jim Ox 144sec. Ran smoothely, consistent DC bias.
wafer 6: production wafer, Jim Ox 144sec. Ran smothely until 50sec, then DC bias dropped. I stopped the run at 60sec and removed the remaining wafers.
This is reminicent of a problem that happened a while back, with intermitent DC bias drop. At that time it was caused by a short across the quartz ring below the wafer in the chamber. Can someone take a look at the quartz ring and see if this is happeneing again? Are there spares on hand?
Thanks,
Chris
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