Numerical Study On Plasma Dynamics Of Capacitive Radio Frequency Discharges At Low Pressure

In addition to the traditional welding,cutting,chemical and other applications,low temperature plasma technology also plays an important role in new technology fields such as semiconductor processing,material surface modification,biomedicine and so on.In recent years,the research of low temperature plasma physics has promoted the rapid development of plasma processing technology,while the application of technology has promoted the in-depth development of low temperature plasma physics research.In the basic experiment and theoretical research of the application of low temperature plasma,the stability of product quality,the clarity of reaction mechanism,and the improvement of yield and efficiency are a series of key problems in the field of new technology.Therefore,a thorough study of its basic physical process and the optimization and improvement of process parameters are particularly urgent.The generation process,property characteristics and motion state of partially ionized gas are the main research contents of low temperature plasma physics.The influence of discharge parameters such as the geometric size of gas discharge device,neutral gas pressure and peak voltage on the characteristics of discharge plasma is a very important physical problem,but it is still not fully studied.It is a simple and efficient method to systematically and deeply study the discharge process and physical characteristics by numerical simulation.In this thesis,a one dimensional fluid model of capacitive radio frequency(RF)argon discharge at low pressure between two parallel plate electrodes is established and the effects of the discharge parameters on the plasma dynamics are studied numerically.The effects of different discharge gaps,neutral gas pressures and peak voltages on ionization and the effects of neutral gas pressure on the dynamic characteristics of plasma discharge parameters are studied.The importance of the ground state excitation process in the electron energy equation is discussed during establishing the plasma fluid model.Numerical solutions are performed for two cases(including and without the ground state excitation process).The numerical results show that the time required for the discharge to reach the steady state is different in the two cases.In addition,without considering the ground state excitation,compared with the case considering the ground state excitation,the ionization rate in the bulk plasma is overestimated,and there are obvious differences in physical quantities such as the period-averaged electron density,ion density,electric field,and electron temperature.Therefore,the ground state excitation is not negligible in the fluid model.Then the effects of different discharge gaps,neutral gas pressures and peak voltages on plasma dynamic characteristics,especially on ionization,are systematically investigated.The effect of neutral gas pressure on the evolutionary characteristics of plasma parameters is studied numerically.It is found that during the evolution of the discharge versus time after reaching the steady state,with the increase of neutral gas pressure,the oscillation amplitudes of electron density,electron current density and total current density at the central point of discharge interval are decreasing,the ion density is basically without oscillation,and the oscillation amplitude of ion current density is increasing;in the powered and grounded sheaths,the oscillation amplitudes of the electron temperature,the ground state ionization collision frequency and the ground state excitation collision frequency are increasing;the electric field and net charge density are increasing at the powered electrode and the grounded electrode.