Pulsed Plasma Sheath Dynamics For Plasma Source Ion Implantation And Glow Discharge

In plasma surface modification, the characteristics of the plasma sheath play a major role in the plasma source ion implantation (PSII) process. A two-dimensional self-consistent fluid model is presented for plasma source ion implantation in the paper. A collisonless ion-fluid model is used to simulate the plasma sheath around the target. The ion-fluid equations of continuity and motion are employed to describe the expansion dynamics of plasma sheath, and the electron density is assumed to obey the Boltzmann relationship. The potential distribution in the sheath is determined by Poisson's equation. The evolutions of the ion density, ion velocity, potential and electrical field are modeled and the ion flux, dose distributions on the target surfaces are calculated. A self-consistent modeling for the low-voltage pulsed direct-current (DC) glow discharge is presented. Particular attention is paid to the time evolution of the discharge from the beginning of a series of voltage pulse applied to the cathode to the steady discharge mode. The dynamics of the discharge and electric characteristics are investigated for N₂ glow discharge. The ionization collisions make the glow discharge a self-sustaining plasma, and the positive ions are accelerated towards the cathode, where they can release secondary electrons upon bombardment.A two-dimensional fluid model is used to compute ion dynamics in the pulsed plasma sheath near the end of a cylindrical bore with and without an auxiliary electrode. The potential, ion density and ion dynamics in the sheath are obtained, and ion flux, dose distributions are calculated by solving Poisson's equation and the equations of ion motion and continuity using finite difference methods. The results indicate that the differences of ion flux and dose among the inner, outer surfaces and the end surface of the bore exist, and the ion focusing causes the nonuniformity of ion flux and dose to come about because of the potential structure in the ion-matrix sheath near the end of the bore. The evolution of the sheath deep inside the bore is in agreement with that presented by one-dimensional model.The ion impact energy and angle distributions at the interior sidewall of a cylindrical bore in the presence of an auxiliary electrode for plasma source ion implantation are determined by means of Monte Carlo method. Because we have made the consideration that the number of ions at different positions of the sheath edge during the sheath edge evolution is different, the contribution of all ions in the bore to the energy and angle distributions is taken into account. Two types of collisions between ions and neutrals charge exchange and elastic collisions are included in the simulation. From the results obtained for various pressures, it can be observed that when the pressure is low, most of the ions in the bore strike the target with highest energy. With the increase of pressure, the mean free path for ions becomes small and more ions will lose energy because of suffering more collisions with neutrals during their route to the target, thereby the number of low-energy ions increases.A two-dimensional fluid model is used to compute ion dynamics in the pulsed plasma sheath of a hemispherical bowl-shaped container with and without an auxiliary electrode, and a two-dimensional unsteady-state heat transfer equation is used to describe the evolution of temperature distribution inside the target. As an example, the ion flux to the target, and energy imparted to the substrate by the ions in the plasma sheath simulation without an auxiliary electrode, and radiative heat loss is used to predict the temperature rise and variation inside the sample in the thermal model. The results show that the temperature near the brim of the bowl is always higher than that near the bottom, and a steady state can be reached after some time. The results also indicate that the time within which the bowl temperature attains equilibrium decreases with the increasing of pulse width while the temperature of the bowl in the steady state increases...