Numerical Investigation Of Sheath Dynamics Behavior In Plasma Source Ion Implantation

Plasma source ion implantation?PSII?,as one special way of surface modifications of cold plasma,is widely used in various industrial production,such as fabrication of semiconductor PN junctions,treatment of wear and corrosion resistance of metal surface,optimization of water and oxygen insulation of insulating materials and so on.In the PSII process,the characteristic of plasma sheath which is formed near the surface of modified material has great influence on the effect of material modification.Therefore,it is necessary to study theoretically the evolution characteristics of sheath at the process of PSII in theory.Combining with the application of PSII technology in insulation material and using the method of numerical investigation,this thesis choose an infinite PET?Polyethylene Terephthalate?cylinder to research.Then it discusses the spatial and temporal evolution of sheath region where ions can be accelerated inside the cylinder in the process of of PSII with nitrogen.In this thesis,a one-dimensional cylindrical hydrodynamic model is used to simulate the evolution of sheath at the inner surface of PET cylinder in PSII.And the equation of surface charging effect on the inner surface in insulating material is considered in the model.The key point of this investigation is that we study the influence of elastic collisions of single ion and double ions with neutral particles respectively,and the influences of main experimental parameters on sheath evolution characteristics are discussed.The results of the study are as follows:1.In the system with only one species of ion implantation,the collision between N₂^?10?andN₂ can significantly reduce the sheath thickness,charge density and ion current density at the inner surface of the PET cylinder.And these time-depend variable curves of ion velocity and ion impact energy at the inner surface of the PET cylinder are not only decreased in value,but also advanced in peak value.These show that collision limit sheath expansion,and the strength of resistance is related to the waveform of external pulse bias.2.In the system with only one species of ion implantation,by changing the external Parameters such as peak value of pulse bias,gas pressure and PET film thickness,the sheath-related parameters such as the sheath thickness,ion impact energy and the accumulated charge density at the inner surface of the PET cylinder will change accordingly.And the gas pressure plays an important role on the evolution of sheath.3.In the system with two species of ion implantation,the changes of ion species ratio have a certain influence on sheath parameters.With the increase of ion ratio ofN^?10?,the sheath thickness will increase accordingly,and the charge density at the internal surface of the dielectric film will also increase,that is,the degree of surface charging effect increases.