Plasma potential control in an inductive discharge

We describe a balanced-phase method to eliminate or control the rf potential differences between inductive plasma sources and ground. Currents from the plasma source to wafer and grounded surfaces are substantially eliminated for ashing or chemical dry etching (CDE) applications. A prototype full-wave helical resonator 8-inch wafer resist stripper using this technique displays high uniformity and a chemical ashing rate over 7 mu/min at 220C in pure O-2,, without device damage. An 11.9kCal activation energy with Arrhenius behavior at the highest rates studied indicate chemical reaction, rather than etchant depletion, was rate-limiting. This new technique can also be applied to ion-enhanced etching processes.