Numerical study of effect of secondary electron emission on discharge characteristics in low pressure capacitive RF argon discharge

Abstract

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 effect of secondary electron emission (SEE) on the discharge characteristics. The model is numerically solved by using a finite difference method and the numerical results are obtained. 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 α-γ-mode.

Numerical study on discharge characteristics influenced by secondary electron emission in capacitive RF argon glow discharges by fluid modeling

“…This is because the secondary electrons gain high energy inside the sheath region, but these secondary electrons are unable to infiltrate to the bulk plasma region because the mean free path of electron is small under the present conditions. [31] Figure 1(c) shows the changes of the cycle-averaged ionization rate with SEE coefficient in a range from 0.01 to 0.3. The results show that the ionization rate has a significant change in discharge as the SEE coefficient increases; it has much higher change in the sheath region than in the bulk plasma region.…”

“…For a better study, we make several assumptions as follows. [31] (i) The diameters of the electrodes are each much greater than the spacing between the two electrodes. Thus the discharge characteristics change only along the x axis.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Its process under ion bombardment plays an important role in the plasma parameters such as electron density, electron temperature, electric field and potential, and ion and electron heating. [20][21][22][23][24][25][26][27][28][29][30][31] Many efforts have been made to explore the effect of SEE coefficient γ. [11][12][13][14][15][16][17][18][19][20] In the simulations and experiments of RF glow discharge studies, the effect of SEE coefficient γ on the sheath structure is very important, since the electron heating on the electrode surfaces is limited by the electric potential.…”

“…[4,5] The studies indicate that the sheath heating of the electrons could be the dominant heating mechanism in RF glow discharges, compared with the secondary electron heating. [23][24][25]31] Though these studies illustrate the discharge mechanisms with considering secondary electrons, the effect of SEE coefficient on the electron heating mechanism or on the discharge sustaining mechanism, which is a key question of RF glow discharge, has not been studied carefully.…”

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“…Again, a strong sensitivity of the simulation results on these surface coefficients was observed and good agreement with experimental measurements was only found for distinct choices of these input parameters. These experimental validation studies and additional computational investigations [7,12,44,[66][67][68][69][70][71][72] show that the discharge characteristics may significantly be influenced by plasma-surface interactions. Therefore, a careful selection of the most important surface processes to be included in simulations and a realistic implementation of these is important for the accuracy of the computational results.…”