Effects of electrode gap on radio-frequency discharge characteristics with a hollow electrode

Abstract

In this paper, the effects of electrode gap on the discharge characteristics in low-pressure argon radio frequency (RF) discharge with a hollow electrode were investigated by a two-dimensional particle-in-cell/MCC model. The results show that the time-averaged electric field, electron density, sheath potential drop, and sheath thickness change with the increasing electrode gap. It is also found that the electron density varies non-monotonically with the electrode gap increasing from 4 to 12 mm due to the different intensities of the hollow cathode effect (HCE) and electron heating at different electrode gaps. The axial sheath at the bottom of the hollow electrode is found to determine the depth of the plasma in the hole and can significantly modulate the intensities of the HCE and electron heating. With the reducing electrode gap, the hole of the hollow electrode is eventually filled with the sheath, and the bulk plasma region is compressed. The results indicate that a small electrode gap is not beneficial to obtain large area plasma with high density outside the hole. Altering the electrode gap can tailor the spatial distribution of the plasma in the RF discharge with a hollow electrode and obtain an optimal electron density.