Time-resolved measurements of ion energy distributions and optical emissions in pulsed radio-frequency discharges

Abstract

In pulse-modulated inductively coupled plasmas generated in CF4:Ar mixtures, a transition between a capacitive coupling mode (E mode) and an inductive coupling mode (H mode) was observed. For a pulsed plasma in a 50%CF4:50%Ar volume mixture with a peak rf power of 200 W at 13.56 MHz and a modulation frequency at 500 Hz with a duty cycle of 95%, the E→H mode transition occurs repetitively 0.75 ms after each rf pulse is applied. This long delay in the mode transition allows us to perform not only time-resolved measurements of optical emission and electrical characteristics but also time-resolved measurements of ion energy distributions at the grounded electrode. These measurements show that a relatively short rf off period can severely perturb the equilibrium plasma state and its recovery may take much longer than the rf off period.