Electron power absorption dynamics and uniformity control in capacitive RF plasmas driven by planar segmented electrodes

Abstract

The effects of segmenting the powered electrode into multiple individually RF driven electrodes on the radial plasma uniformity control in capacitive plasmas is investigated based on two-dimensional kinetic simulations. At moderate pressures, where density peaks arise at the electrode edge due to enhanced local electron heating, the plasma uniformity is significantly improved by employing segmented electrodes and applying a higher voltage amplitude to the central powered electrode relative to the outer ring electrode. In contrast, at low pressures, at which non-local electron dynamics dominates and a center-high density profile forms, increasing the voltage amplitude at the outer ring electrode fails to enhance uniformity. This is caused by the pronounced radial electron transport during the phase of sheath expansion at the powered electrodes. Due to the sheath potential difference at each electrode segment, electrons above the outer ring electrode experience not only upward acceleration, but also a strong inward radial acceleration during sheath expansion, which further increases the plasma density at the center and reduces the uniformity. Instead of setting different voltage amplitudes, increasing the driving frequency at the outer ring electrode is found to significantly enhance electron heating above this electrode segment via more frequent and rapid sheath oscillations, leading to improved plasma uniformity. Furthermore, the impact of segmented electrodes on the radial uniformity of the ion energy and incidence angle at the electrode surface is examined. Applying different voltage amplitudes to the electrode segments is found to induce substantial radial nonuniformities of the mean ion energy and incidence angle, whereas applying different frequencies to each segment maintains uniformity of these parameters under the discharge conditions studied in this work.