Hi Pramod,

The polymer deposition that arises due to the use of CHF3 and SF6
change the characteristics of the chamber, and the system may have
difficulty automatically adjusting/tuning to match during a run - you
can imagine there could be a lag between the system RF adjustment and
the changing RF characteristics of the substrate + chamber. When the
system is not matched, the plasma cannot sustain itself. Another
possible problem is deposition of a 'bridge' of material between the
substrate electrode and the ground electrode that runs around its
circumference, separated by a millimetre or so. Narrowing of the
electrode-ground gap can lead to an RF short and lead to grounding of
the system. In worst case the plasma extinguishes altogether, but it
is likely that with moderate shorting between electrode and ground a
flickering plasma could result and sustain itself. If you increase the
O2 concentration in the flow, this could reduce the polymer build-up
rate and reduce/eliminate the flickering.

Bottom line: clean your chamber after each run (manual clean, removing
the substrate and ground and completely, removing any material
between). If you still experience problems, contact Oxford Instruments
customer service and relay your problems to them. That's what they're
there for - don't let them get away with it! ;)

Rest assured, the problems you have reported here are very common in
the RIE community, so OI should be able to diagose the problem and
recommend the best (user tested) solution right away.

Good luck!

Michael


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Question:
Does any one know what could be the reasons for Plasma Flickering in
Oxford Plasmalab 80 Plus RIE system?. I am trying to etch polymers
with SF6/O2/CHF3 gas chemistry at 30mTorr, 200W. The recipe was
working perfect earlier. Pure O2 plasma, even at 30mTorr, does not
flicker at all. It starts flickering when you mix O2 with SF6 and/or
CHF3. What could be the reasons?