Numerical Study On Physical Characteristics Of Plasmas In RF Argon Glow Discharge At Low Pressure

Glow discharge plasma process in line with environmental protection and modern technology, and the cost of equipment and maintenance is low, so it is widely used in microelectronics industry for plasma etching and film deposition, plasma chemistry, surface modification of various materials, medical tool sterilization, environmental protection and many other fields of science and technology. Glow discharge is easily obtained at low pressure due to its low breakdown voltage compared with the atmosphere pressure gas discharge or other high pressure gas discharge for which relatively higher RF power and breakdown voltage are required. In addition, low pressure glow discharge is relatively uniform and stable, and the transition to arc discharge or filamentary discharge will not happen.Because plasma is more complex than non-ionized gas, and there are still many relevant internal mechanisms have not been understood fully, especially in the aspect of electron heating mechanism. In order to improve the efficiency of the application of low temperature plasma, it is necessary for us to make a detailed study of various plasma physical parameters. Based on the drift and diffusion approximation theory, a 1D fluid model on capacitively coupled RF argon glow discharge at low pressure is established to study the discharge characteristics.In this dissertation we have mainly studied for two aspects. First of all, we obtained some primary results, such as, the cycle-averaged spatial electric field, potential, electron temperature, electron density, ion density and ionization rate varing as a function of diacharge RF cycles. More important, with the increasing discharge time, the spatial distribution of cycle-averaged electron net power absorption, electron heating rate, electron convective term and electron power dissipation has also been obtained. Experimental study can benefit from the results of numerical research.The mechanism of electron heating largely depends on a wide range of discharge conditions:gas pressure, excitation frequency and voltage, electrode gap and so on. While, the effect of secondary electron emission (SEE) coefficient, as a very important parameter in glow discharge, on the electron heating mechanism has not been researched carefully. So, in the second part of this work, we studied the influence of SEE coefficient on the discharge characteristics of low pressure RF argon glow discharge. The numerical results indicate that when the SEE coefficient is larger, the plasma density is higher and the time of reaching steady state is longer. It is also found that the cycle-averaged electric field, electric potential, and electron temperature change a little as the SEE coefficient is increased. Moreover, the discharge characteristics in some nonequilibrium discharge processes with different SEE coefficients have been compared. The analysis shows that when the SEE coefficient is varied from 0.01 to 0.3, the cycle-averaged electron net power absorption, electron heating rate, thermal convective term, electron energy dissipation, and ionization all have different degrees of growth. While the electron energy dissipation and ionization are quite special, there appear two peaks near each sheath region in the discharge with a relatively larger SEE coefficient. In this case, the discharge is certainly operated in a hybrid a-y mode.