Problem drytek2 2001-02-12 11:39:50: plasma changing color

[ericp at snf.stanford.edu]

I've experienced several strange etches:
Last week, in the middle of an etch (nitride etch), the plasma 
changed color (at about 6 minutes), from a normal "purple"
to a brownish color.  This was sudden.  Restarting the 
machine cleared the problem.  I ran it again on the weekend andexperienced the same behavior.  
I ran a long O2 descum on it Saturday. Problem not seen since,
but users should watch plasma carefully for critical etches. 
When this occured, the only visible symptoms were plasma
color change and reflected power jump.  Gas flows and 
pressure indicated steady and correct.