Particle Simulation Of Sheath Characteristics With Dielectric Target In Plasma Immersion Ion Implantation

Plasma immersion ion implantation (PⅢ) is a new ion implantation technology based upon the traditional ion-beam ion implantation (PBII) technology, as PⅢ has many advantages such as low costs, simple equipment, easily operation and is capable to process the work-piece with complex shape. Presently, PⅢ technology has been widely used in the modification of materials, semiconductor treatment, and microelectronic materials processing, etc. However, when treating the dielectric substrate with PⅢ, the implanted ions can accumulate at the dielectric surface owing to the low electric conductivity of the dielectric materials, and this result in the charging effects. So the implanted ions can’t get the full acceleration with the same amplitude of the applied negative pulse. What’s more, with the time extend, the converging plasma sheaths from the inner surfaces of the cylindrical dielectric tube could get overlapping in the central axis, the implanted dose and energy decrease further. In order to solve these problems, it is necessary to sduty theoretically the sheath evolution near the inner of the cylindrical dielectric tube during the PⅢ processing. Because the implanted ions mainly get acceleration from the plasma sheath, the characteristics of the plasma sheath directly affect the final properties of the target materials after PⅢ process. With the theoretical investigation, the physical mechanism of ion implantation can be revealed, and the results can give some guidance for the optimization of an actual PⅢ process.In this thesis, we adopt the particle-in-cell method to study the principles of the sheath expansion and implantation characteristics in PⅢ process with a dielectric target. The influences of many parameters on the PⅢ are discussed. The thesis is organized as:In Chapter1, we briefly introduce the characteristics and applications of PⅢ technology, the current research state and significance of the PⅢ in flat and cylindrical dielectric materials, and also review the investigation methods of computer simulation for PⅢ.In Chapter2, we give a detailed description about the Particle-In-Cell plus Monte Carlo Collision (PIC/MCC) method which is used in plasma computer simulation. We divide the PIC/MCC method into two parts, and introduce the PIC and MCC method, respectively. At the same time, we also make a corresponding derivation of the one-dimension flat plate model and two-dimension cylindrical model.In Chapter3, the sheath expansion near the inner surface of a cylindrical dielectric tube is investigated by using a two-dimension hybrid PIC model. The influence of experimental parameters (such as the metal electrode length and dielectric thickness) on the uniformity of implanted ions dose and energy along the inner surface of the dielectric tube is analyzed and discussed. It finds that during the PⅢ process, as there are increasingly amount of charges accumulate on the dielectric surface, the charging effect become much more significant, leading a lower surface potential and lower implanted energy. Secondly, with a finite length cylindrical dielectric tube, the distribution of the implanted ion dose along the inner surface is nonuniform, the implanted dose near the top of the bore is much bigger than the other region. When all the ions inner the tube get implanted, many ions originate from outside of the bore continued to implant into the inner surface, this make the nonuniformity of the implanted dose more serious. So, it is very important for improving the implanted dose uniformity to end a single pulse period before all of the ions in the tube get exhaust. At last, the implanted ions energy distribution uniformity along the inner surface of the dielectric tube can been improved by using a longer metal electrodeIn Chapter4, In order to overcome the shortage of hybrid PIC in the simulation of a nanosecond pulse PⅢ (in the hybrid PIC model, electrons are supposed to be Boltzmann’s distribution and thus lack the movement effect of electrons to PⅢ), we employ a self-consistent PIC/MCC model to study PⅢ to PET substrate. With the model, ions and electrons are both dynamically traced simultaneously. The various collision processes of electrons collision and the secondary electron emission (SEE) on the surface of PET substrate are included. We have studied the influence of the thickness of dielectric film and the gas pressure on PⅢ. The simulation results demonstrate that it is necessary to use a lower pressure and thinner PET substance to get better PⅢ property in PⅢ of dielectric film.