Functional separation of biasing and sustaining voltages in two-frequency capacitively coupled plasma

Separation of the effects of rf sources used for biasing the wafer and for sustaining the plasma is studied by measuring the space profiles of net exc itation rate of Ar(3p(5)) for a two-frequency capacitively coupled plasma a s a representation of a typical oxide etcher. Measurements were performed i n Ar and in CF4/Ar mixtures. For biasing supply operating at low frequency, 700 kHz, it was shown that the effect of the voltage becomes significantly smaller as the sustaining voltage is changed from high frequency, 13.56 MH z, to very high frequency (VHF), 100 MHz, and it even disappears for pulsed operation in mixtures. This is the result of the low dc self-bias at the V HF electrode that allows the high energy secondary electrons to leave the p lasma without excessive contribution to ionization and dissociation. (C) 20 00 American Institute of Physics. [S0003-6951(00)03330-1].