高低频不同电压条件下腔室内CCP冷等离子体源的仿真分析

等离子体的状态的变化特征，特别是在双频情况下，是PECVD工艺设备的一项重要指标，这促使人们用不同的方法对它们进行研究。本文使用CFD-ACE 商业软件建立了二维流体模型对N2等离子体进行仿真。首先在高频13.56MHz，高频电压300V，低频电压0V的条件下描述了等离子体，特别是在鞘层部位的电势、电子数量密度、氮自由基和电子温度，分布的基本特征。在此基础上，讨论了高频电压分别是200V,300V,400V时及低频0.3MHz,低频电压分别是500V,600V,700V时对等离子体密度的影响。结论表明，在电极表面形成了约3mm厚的鞘层，在鞘层内电势和电子温度随时间和空间变化较大，而在非鞘层区域内电势跟随电极电压的变化而变化，但几乎不随空间变化，电子温度也只在很小的范围内变化。氮自由基的数量密度也受射频电压的调制，但相对变化很小。等离子体密度仅在鞘层区域内随时间发生变化，所以通过比较主等离子体区参数可以看出，等离子体的密度随着高频电压升高，随低频电压的升高略有下降，同时x方向和y方向的均匀性将会发生变化。因此，在其他条件不变的情况下需要选择合适的高低频电压来获得高密度和均匀性均合乎要求的等离子体。

Simulation of cold plasma in a chamber under high- and low-frequency voltage conditions for a capacitively coupled plasma

The characteristics of cold plasma, especially for a dual-frequency capacitively coupled plasma (CCP), play an important role for plasma enhanced chemical vapor deposition, which stimulates further studies using different methods. In this paper, a 2D fluid model was constructed for N₂ gas plasma simulations with CFD-ACE+, a commercial multi-physical software package. First, the distributions of electric potential (E_pot), electron number density (N_e), N number density (N) and electron temperature (T_e) are described under the condition of high frequency (HF), 13.56 MHz, HF voltage, 300 V, and low-frequency (LF) voltage, 0 V, particularly in the sheath. Based on this, the influence of HF on N_e is further discussed under different HF voltages of 200 V, 300 V, 400 V, separately, along with the influence of LF, 0.3 MHz, and various LF voltages of 500 V, 600 V, 700 V. The results show that sheaths of about 3 mm are formed near the two electrodes, in which E_pot and T_e vary extensively with time and space, while in the plasma bulk E_pot changes synchronously with an electric potential of about 70 V and T_e varies only in a small range. N is also modulated by the radio frequency, but the relative change in N is small. N_e varies only in the sheath, while in the bulk it is steady at different time steps. So, by comparing N_e in the plasma bulk at the steady state, we can see that N_e will increase when HF voltage increases. Yet, N_e will slightly decrease with the increase of LF voltage. At the same time, the homogeneity will change in both x and y directions. So both HF and LF voltages should be carefully considered in order to obtain a high-density, homogeneous plasma.