Problem drytek2 2004-02-29 10:19:39: Plasma unstable

[kenney at snf.stanford.edu]

When using Process #2 Poly Etch or Process #3 Nitride Etch
the system will run perfectly for a few minutes, then the plasma will deignite in either all plates or in the 3rd plate from the top.
It is easy to retune the RF to get back a perfect plasma condition, but it becomes unsatble within a few minutes and the 
plasma deignites again.