Hybrid Plasma Simulation of RF Hollow Cathode Discharge at Moderate Pressure

  Plasma sources consisting of radio-frequency (RF) hollow cathode discharges (HCD) at moderate pressures have gained significance for advanced plasma processes. HCDs form in cylindrical cavities in the cathode. An array of such cavities can be used to create a large area HCD source. Under certain conditions the plasma in the hollow cavities becomes more intense. In this study, a single hollow cathode hole is simulated using a hybrid plasma model. The model includes continuity equations for charged and neutral species, drift-diffusion approximation for electron flux, the momentum conservation equation for ions, and the Poisson equation. A Monte Carlo model for secondary electrons is used to accurately compute production rates of species, which are coupled to the fluid plasma model. RF HCD behavior is simulated for different hollow cathode hole design and operating conditions. The plasma penetration inside the hollow cathode hole is enhanced depending on the pressure and hole size. The plasma enhancement due to RF sheath heating with increase in frequency as well as secondary electron emission has been explored synergistically. Additionally, the effect of the area ratio of the powered electrode to the grounded electrode on RF HCDs has been investigated.