Mechanism Of Radio-frequency Hollow Cathode Discharge

Radio-frequency hollow cathode discharge(RF-HCD) is widely used for thin films deposition and material processing due to the high density and low energy plasma. In this thesis, the discharge of RF-HCD were studied by experiments and simulation, with special emphasis on the mechanism of electron heating in radio frequency discharge.Firstly, the discharge characteristics of RF-HCD in a cylindrical hollow cathode in argon is investigated. The image of discharge plasmas, the density of electrons and the electron energy probability distribution function(EEPF) curve are measured under different conditions. The results show that the discharge characteristics are influenced by the discharge voltage, the gas pressure, the hole diameter and the frequency.Secondly, the RF-HCD was simulated by a 2D fluid model. The spatial and temporal distribution of the electron density, the ion density, the ionization rate, the electric potential and the electric field are calculated. The results show that with voltage increase, the electric field in the sheath layer enhances, and the ionization rate and plasma density increase. As the gas pressure increasing, the sheath layer becomes thinner and the plasma density increases. Increasing voltage frequency is helpful for improving plasma density.Thirdly, the influences of voltage, frequency, gas pressure and hole diameter on the sustaining mechanism of RF-HCD have been studied. When the voltage increases, the electron heating mechanism transits from ohmic heating to collision-free stochastic heating,and the influence of the second electron emission from the cathode becomes remarkable. At pD≤0.3Torr?cm, the mechanism is stochastic heating predominantly; while at pD0.3Torr?cm, the predominant energy mechanism is ohmic heating. Increasing frequency helps electrons obtaining more energy from the electric field, resulting in the mechanism changing from ohmic heating to stochastic one.