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中国物理学会期刊

脉冲射频容性耦合氩等离子体的发射探针诊断

CSTR: 32037.14.aps.69.20191864

Diagnosis of capacitively coupled plasma driven by pulse-modulated 27.12 MHz by using an emissive probe

CSTR: 32037.14.aps.69.20191864
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  • 利用工作在浮点模式下的发射探针, 对500 Hz脉冲调制的27.12 MHz容性耦合氩气等离子体的空间电位和电子温度的时变特性进行了诊断. 等离子体空间电位是通过测量强热状态下的发射探针电位获得的, 而电子温度则是由发射探针在冷、热状态下的电位差来估算得到. 测量结果表明: 脉冲开启时, 空间电位会快速上升并在300 μs内趋于饱和; 当脉冲关断后, 空间电位经历了快速下降后趋于稳定的过程. 电子温度在脉冲开启时存在过冲并趋于稳定的特征; 而在脉冲关断期间, 电子温度在300 μs内则快速下降到0.45 eV后略有上升. 无论在脉冲开启或关断期间, 空间电位基本上都随功率和气压的变化存在有线性的依赖关系; 而放电功率对脉冲开启期间过冲电子温度与稳态电子温度差异的影响较大. 针对空间电位和电子温度在各阶段及不同放电条件下的时变特性, 给出了相应的解释.

     

    There are several methods of diagnosing the capacitively coupled plasma, such as microwave resonance probe, Langmuir probe, etc, but methods like microwave resonance probe are mainly used for determining the electron density. Moreover, in the diagnosing of plasma potential, the emissive probe has a higher accuracy than the traditional electrostatic probes, and it can directly monitor the potential in real time. However, in the existing work, emissive probe is mostly applied to the diagnosis of plasmas with high density or plasmas modulated by pulsed dual frequency (one of the radio frequency sources is modulated), the experiments on the emissive probe diagonising plasma excited by a pulsed single frequency are quite rare. In this paper, the temporal evolution of the plasma potential and electron temperature with input power and pressure in a pulsed 27.12 MHz capacitively coupled argon plasma are investigated by using an emissive probe operated in floating point mode. The plasma potential is obtained by measuring emissive probe potential under a strongly heated condition, while the electron temperature is estimated from the potential difference between the emissive probe under strongly heating and cold conditions. The measurements show that as the pulse is on, the plasma potential will rise rapidly and become saturated within 300 μs due to the requirement for neutrality condition; while the pulse is off, the plasma potential undergoes a rapid decline and then stabilizes. An overshoot for the electron temperature occurs as the onset of the pulse, because of the influence of radio frequency electric field and residual electrons from the last pulse; during the pulse-off time, rapid loss of high-energy electrons causes the electron temperature to rapidly drops to 0.45 eV within 300 μs, then it rises slightly, which is related to the electrons emitted by the probe. The plasma potential basically has a linear dependence on the change of input power and pressure for the pulse-on and pulse-off time; and the input power has a greater influence on the difference between the overshoot electron temperature and the steady state electron temperature during the pulse-on time. Corresponding explanations are given for the temporal evolution of plasma potential and electron temperature in different pulse stages and under different discharge conditions.

     

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