Ion Dynamics Of Plasma Source Ion Implantation In The Sheath Of A Hemispherical Bowl-Shaped Vessel

Plasma source ion implantation (PSII) has been widely used in surface modification and semiconductor fabrication. In its practical application, plasma shealth evolution has a significant influence on the interaction between plasma and the surface of materials.In this thesis, two-dimensional fluidic model was utilized to simulate the sheath evolutions during PSII process. Detailedly, the collisionless ion-fluid model was used to simulate the plasma sheath around the sample. The ion-fluid equation of continuity and motion were 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 ion dynamics in the pulsed plasma sheath of a hemispherical bowl-shaped container were investigated, with or without an auxiliary electrode at the center. The potential, ion flux and ion dose distributions were calculated by finite difference methods. The obtained results indicate that the ion flux and the implanted ion dose among the inner and outer surfaces near the bowl edge are significantly nonuniform. This may be attributed to the ion focusing induced by the deformation of the potential structure. We found that the uniformity of ion dose on the inner surface could be improved by using short voltage pulse or by adding an auxiliary electrode at the spherical center. We believe this work would be very helpful to the design of practical plasma source ion implantation processes.The influences of the electrode size and the container thickness upon the ion dose distribution were also investigated. The results show that the ion dose on the inner surface decreases with the size of auxiliary electrode. The ion dose on the brim surface also diminishes with the bowl thickness obviously while that on inner and outer surface decrease slightly.