Hollow cathode effect in radio frequency hollow electrode discharge in argon

Abstract

Radio frequency capacitively coupled plasma sources (RF-CCPs) with hollow electrodes can increase the electron density through the hollow cathode effect (HCE), which offers a method to modify the spatial profiles of the plasma density. In this paper, the variations of the HCE within one RF period were investigated by a two-dimensional particle-in-cell/Monte-Carlo collision (PIC/MCC) model. The results show that the sheath electric field, the sheath potential drop, the sheath thickness, the radial plasma bulk width, the EEDF, and the average electron energy in the cavity vary within one RF period. During the hollow electrode sheaths expansion phase, the secondary electron heating and sheath oscillation heating in the cavity are gradually enhanced, and the frequency of the electron pendular motion in the cavity gradually increases, hence the HCE is gradually enhanced. However, during the hollow electrode sheaths collapse phase, the secondary electron heating is gradually attenuated. In addition, when interacting with the gradually collapsed hollow electrode sheaths, high-energy plasma bulk electrons in the cavity will lose some energy. Furthermore, the frequency of the electron pendular motion in the cavity gradually decreases. Therefore, during the hollow electrode sheaths collapse phase, the HCE is gradually attenuated.