Particle-in-cell modeling of low-pressure radio frequency hollow cathode discharge

Hollow cathode discharge (HCD) is an attractive option to generate high-density plasmas using both direct current and radio frequency (RF) sources. Positive ions bombarding the surfaces produce secondary electrons and the electrons' pendulum motion between the opposite cathode surfaces enhances ionization in the hollow cathode region. As a consequence of this, HCD can be sustained with a lower voltage than regular discharges with plane electrodes. The efficiency of HCD in producing high density plasma makes it attractive in several applications, including plasma processing, plasma propulsion, and spectrochemistry. In this study, we are focused on an argon RF capacitive discharge with trenches in the cathode. This device is operated between 5 to 15 Pa targeting material deposition process conditions. Due to the low pressure and high electric field gradient, a 2d3v particle-in-cell modeling is employed to provide a fully kinetic description of electrons' and ions' motion. The applied voltage, electron secondary emission coefficients and electron reflection coefficients are varied to study their influence on electron heating, ionization and composition of current. The simulation results are compared to the experimentally measured spatio-temporal emission intensity of excited species, and plasma density obtained with the hairpin resonator probe. Where differences between the model and experiments are observed, potential improvements of the model are discussed.