Effects of fast atoms and energy-dependent secondary electron emission yields in PIC/MCC simulations of capacitively coupled plasmas
Effects of fast atoms and energy-dependent secondary electron emission yields in PIC/MCC simulations of capacitively coupled plasmas
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DOI：
10.1088/0963-0252/24/3/034002
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发表时间：
2015-05-01
影响因子：
3.8
通讯作者：
Schulze, J.
中科院分区：
文献类型：
--
作者：
Derzsi, A.;Korolov, I.;Schulze, J.
在大多数射频电容耦合等离子体 (CCP) 的 PIC/MCC 模拟中，通常会进行一些简化：(i) 不追踪快速中性子，(ii) 忽略重粒子引起的激发和电离，(iii) 不考虑由于中性粒子撞击而从边界表面产生的二次电子发射，以及 (iv) 假设二次电子发射系数为常数，即 与入射粒子能量和表面条件无关。在这里，我们在等离子体处理应用的典型条件下检查这些简化的有效性。我们研究了在氩气中、频率为 13.56 MHz、中性气体压力为 5 Pa 至 100 Pa 的 CCP 模拟中，包含快中性粒子以及对离子和快中性粒子使用实际的能量相关二次电子发射系数的影响。我们发现，当模拟中实际包含重粒子时，在大多数情况下，等离子体密度和到电极的离子通量都会增加。发现护套宽度更小，并且发现模拟在高压、高电压幅度下出现发散，与实验结果定性一致。通过在模拟中打开和关闭各个过程，我们确定了它们对电离动力学和等离子体参数的单独影响。虽然发现重粒子过程的气相效应在大多数情况下是中等的，但有效二次电子产额的自洽计算被证明在 CCP 模拟中非常重要，以便产生真实的结果。
In most PIC/MCC simulations of radio frequency capacitively coupled plasmas (CCPs) several simplifications are commonly made: (i) fast neutrals are not traced, (ii) heavy particle induced excitation and ionization are neglected, (iii) secondary electron emission from boundary surfaces due to neutral particle impact is not taken into account, and (iv) the secondary electron emission coefficient is assumed to be constant, i.e. independent of the incident particle energy and the surface conditions. Here, we examine the validity of these simplifications under conditions typical for plasma processing applications. We study the effects of including fast neutrals and using realistic energy-dependent secondary electron emission coefficients for ions and fast neutrals in simulations of CCPs operated in argon at 13.56 MHz and at neutral gas pressures between 5 Pa and 100 Pa. We find an increase of the plasma density and the ion flux to the electrodes under most conditions when heavy particles are included realistically in the simulation. The sheath widths are found to be smaller and the simulations are found to diverge at high pressures for high voltage amplitudes in qualitative agreement with experimental findings. By switching individual processes on and off in the simulations we identify their individual effects on the ionization dynamics and plasma parameters. While the gas-phase effects of heavy particle processes are found to be moderate at most conditions, the self-consistent calculation of the effective secondary electron yield proves to be important in simulations of CCPs in order to yield realistic results.