Diagnostic study and simulation of capacitive coupled RF plasma
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摘要: 针对中等气压、中等功率下射频容性耦合(CCRF)等离子体的放电特性，采用基于流体模型的COMSOL软件仿真，建立一维等离子体放电模型，以Ar为工作气体，研究同一气压时不同射频输入功率下等离子体电子温度和电子密度的分布规律。同时依据仿真模型设计制作相同尺寸的密闭玻璃腔体和平板电极，实验测量了不同射频输入功率时放电等离子体的有效电流电压及发射光谱，进而计算等离子体的电子温度及电子密度；利用玻耳兹曼双线测温法，得到光谱法下等离子体的电子温度及电子密度。结果表明：当气体压强为250 Pa、输入功率为100~450 W时，等离子体电压电流呈线性关系，电子密度随功率的增大而增大，而电子温度并未随功率的变化而有明显变化，其与功率无关。运用仿真模拟验证了实验的准确性，通过比较，三种方法所得的结果相近。通过结合等效回路法、光谱法和数值模拟仿真法初步诊断出中等气压下等离子体的放电参数，提出了结合三种方法作为实验研究的方法，使实验结果更具说服力，证明其方法的可靠性，也为进一步的等离子体特性研究提供依据。
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关键词:
- 容性耦合射频放电 /
- 等离子体 /
- COMSOL仿真模拟 /
- 光谱法诊断 /
- 等效电路法
Abstract: Aiming at the discharge characteristics of radio frequency capacitively coupled (CCRF) plasma at moderate pressure and medium power, a one-dimensional plasma discharge model was established by using COMSOL software based on fluid model. The distribution law in plasma electron temperature and electron density were studied at the same pressure and different radio frequency input power with Ar gas as working gas. At the same time, a closed glass cavity and a flat plate electrode of the same size were designed and fabricated according to the simulation model. The effective current, voltage and emission spectrum of the discharge plasma were measured experimentally at different RF input power. The electron temperature and electron density of the plasma were calculated by the current-voltage relationship and the energy balance equation. The electron temperature and electron density of plasma were obtained by Boltzmann double-wire method. When the gas pressure was 250 Pa and the input power was 100-450 W, the plasma voltage and current showed a linear relationship. The electron density increased with the increase of the power, but the electron temperature did not change with the change of the power. At the same time, the accuracy of the experiment was further verified by simulation. In this paper, the discharge parameters of plasma at moderate pressure are preliminarily diagnosed by combining the equivalent circuit method, spectral method and numerical simulation method, and a combination of these three methods is proposed for experiment to make the experimental results more convincing and to provide a basis for further study of plasma characteristics. -
图 1 容性耦合射频氩等离子体的制备及诊断实验装置
Figure 1. Preparation and diagnostic experiment device of capacitive coupled RF argon plasma
图 2 气压为250 Pa时不同输入功率下的电流电压图
Figure 2. Current and voltage images with different input power at 250 Pa
图 3 气压为250 Pa时电压随电流的变化关系曲线
Figure 3. Relationship between voltage and current when the air pressure is 250 Pa
图 4 气压为250 Pa时电子密度随电流及功率的变化关系曲线
Figure 4. Relationship between electron density and current and power when air pressure is 250 Pa
图 5 气压为250 Pa时电子温度随电流以及功率的变化关系图像
Figure 5. Relationship between electron temperature and current and power when air pressure is 250 Pa
图 6 气压为250 Pa，功率为350 W时极板中心处测得的波长范围为790~830 nm的发射光谱
Figure 6. Emission spectra at the center of the plate at 250 Pa atmospheric pressure and 350 W power ranging from 790 nm to 830 nm
图 7 250 Pa时电子密度随功率以及电流的变化关系图像
Figure 7. Relationship between electron density and power and current at 250 Pa
图 8 250 Pa时电子温度随功率以及电流的变化关系图像
Figure 8. Relationship between electron temperature and power and current at 250 Pa
图 10 仿真模拟下电子温度随距离变化的分布情况
Figure 10. Simulation of the distribution of electron temperature with distance
图 11 仿真模拟下电子密度随距离变化的分布情况
Figure 11. Distribution of electron density versus distance under simulation
图 12 仿真模拟与实验所得的电子密度的比较图
Figure 12. Comparison of electron density obtained from simulation and experiment
表 1 气体为氩气时的几条特征谱线所对应的激发能、统计权重和跃迁几率
Table 1. Excitation energy, statistical weight and transition probability corresponding to several characteristic lines of argon gas
λ/nm E/eV G A/(×107 s-1) 811.5 13.08 7 3.31 826.5 13.33 3 1.53 476.5 19.87 4 6.4 457.3 19.87 4 4.71 663.8 19.61 4 1.37 617.2 19.61 6 2 
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表 2 实验与模拟的电子密度结果的比较
Table 2. Comparison of electron density between experiment and simulation
P/W current voltage method/m-3 electron density/m-3 simulation spectroscopy 100 5.20×1016 3.90×1016 5.59×1017 200 8.08×1016 4.50×1016 9.14×1017 300 1.02×1017 9.18×1016 1.76×1018 400 1.33×1017 1.00×1017 2.57×1018
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