The chamber may also be dirty.  You might consider doing a plasma clean on it.
Usually this is O2 etch with a bare wafer for 5-10min at 600W.

-Mike
  U. of Louisville

>>> "Bob Henderson"  6/10/2009 12:05 PM
>>> Sounds like you have a leak in your system. If everything is working fine
>>> you should have a light blueish plasma while ashing. Bob Henderson