Numerical Studies On The Influence Of Secondary Electrons And Gas Pressure On Plasma Characteristics In RF Capacitive Discharges At Low Pressure

Capacitively Coupled Plasmas(CCP)technology is of great application to the plasma etching systems and the plasma surface modification,therefore,it has been a hot topic for a long time.It has been applied to many prosesses,such as for Plasma Enhanced Chemical Vapor Deposition systems.With the widespread application of CCP,many new challenges need to be faced.For example,more demands for the etching efficiency and the anisotropy of etching technology,while the traditional single frequency CCP technology cannot achieve the independent control of the ion density and energy.Based on a goal of growing demands for materials processing and surface modification,the current solution to this problem is to use a dual frequency discharge to generate the plasma.In the processing of dual-frequency CCP.the high frequency are used to adjust the ions density of plasmas,and the low frequency are able to modulate the ion energy in the plasma sheath.The various discharge parameters in the dual-frequency discharge,especially the dual-frequency,the gas pressure and so on,have a crucial influence on the discharge characteristics.So,deep research on these effects will help to further improve the production process.In this paper,a numerical simulation method is used to study the CCP discharge process of argon glow an low pressure,furthermore,the influence of the gas pressure and the dual frequency on the physical quantity in the discharge is systematically investigated.There are two different mechanisms for heating electrons in CCP discharges:electron pressure heating and electron ohmic heating.The mechanism of the electron heating largely depends on a wide range of discharge conditions,such as,electrode gap.gas pressure,driving frequency,applied voltage and so on.In this paper,except researching the effects of Secondary Electron Emission(SEE)on electric field,electric potential and electron temperature,we also focus on the profound influence of SEE on electron heating of pressure electron heating and ohm electron heating.In this paper,the contents in each chapter are as follows:Chapter 1 is the introduction.It introduces the principle of grow discharge,the history and the present conditions of CCP technology.In chapter 2,according to the plasma fluid theory,a one dimensional fluid model is established for CCP and numerical simulation is carried out under the drift diffusion approximation.First,the equations are unidimensional,and the initial conditions and boundary conditions are given according to the characteristics of the established model.Second,in order to calculate the stability and accuracy of computer,the equations are dimensionless.Third,the finite difference methods are used to solve the equations.At last,using Fortran language for programming calculation results.In chapter 3.a 1D fluid model of CCP argon glow discharges at low pressure is employed.The influence of SEE on the plasma characteristics is investigated numerically by the model.The results show that,SEE almost has no effect on the cycle-averaged electric field,and has little effect on the cycle-averaged electron temperature in the bulk plasma.but has obvious effect in the two sheath regions;Also,SEE has influence on the cycle-averaged ionization rate,electron density,electron current density,ion current density and total current density,electron energy loss,electron pressure heating,electron ohmic heating,electron heating and ion heating in the whole discharge region,and the variations in sheath regions are stronger than in plasma region.In chapter 4.a ID fluid model for dual radio frequency CCP argon capacitive glow discharges at low pressure is established.The results are analyzed to study the effects of gas pressure on the plasma characteristics.It shows that the gas pressure has effect on the cycle-averaged plasma density and the ionization rate increase and the cycle-averaged ion current densities and ion energy densities on the electrodes electrode.The cycle-averaged electric field has a complex behavior with the increasing gas pressure,and its changes take place mainly in the two sheath regions.The cycle-averaged electron pressure heating,electron ohmic heating,electron heating.and electron energy loss are all influenced by the gas pressure.And there appear two peaks of the electron heating in the sheath regions and the two peaks become larger and move to electrodes as the gas pressure increases.In chapter 5.based on a one-dimensional fluid model,we investigate dual frequency CCP argon discharge sustaining,and determine the influence of the low and high frequency sources on the plasma parameters.The results show that all the cycle-averaged plasma parameters in steady state are symmetric in space.The low frequency has no effects on the electron density,the electron temperature,the electric field,the potential and the ionization rate.But,in the sheath regions,the low frequency has effect on the electron pressure heating,electron ohmic heating and the electron heating.The high frequency has a little effects on the electron temperature,the electric field and the potential.But,the electron density,the ionization rate,the electron pressure heating,the electron ohmic heating and the electron heating increase as the high frequency increases.Finally,a brief summary ends this thesis.