Ion energy uniformity in high-frequency capacitive discharges

Ion energy distribution functions and ion fluxes in low-pressure, high-frequency (13.56-80 MHz) capacitive discharges were investigated both theoretically and experimentally. In most of the conditions explored, the ion energy distribution function was a single peak centered at the time-averaged plasma potential. Lower energy ions with higher fluxes are obtained as the frequency increases. The uniformity of the ion energy across large-area electrodes (40 cm2) was also studied in conditions under which the standing wave effect is important, i.e., conditions such that the rf voltage and the ion flux are strongly nonuniform. Unlike the latter quantities, the ion energy was uniform across the reactor at all frequencies, due to dc current flowing radially in the plasma and in the electrodes.