I'm depositing a 1.2-1.3 micron  PECVD oxide layer with a
Plasma Therm  ETP-3       I am getting excellent uniformity and
rate of 200 angs/min OCCASIONALLY.  Then the rate and
uniformity gradually or abruptly goes to hell.

Question: what is the order of influence of each variable?
ie Temperature of pallet                 (250C)
  Process pressure                      (600mTorr)
  Power                                 (20W)
  N2 flow                               (600sccm)
  N2O flow                              (600sccm)
  5% SiH4 flow                          (630sccm)

PS we have found several major leaks which are being addressed.
   Would this cause intermittent successful episodes?

Any information or direction is gratefully appreciated.
Liz Shelley
Process Development Engineer
MicroMetrics, Inc
Londonderry, NH