对功率电极处直流鞘层中加速电子产生的高压容性耦合等离子体的研究
Investigation of high pressure capacitively coupled plasmas produced by electrons energized in DC sheath at powered electrode
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中文总结 AI 辅助
研究人员实验探究宽压力范围下容性耦合等离子体的功率吸收机制，发现除低压外，更高压力下射频场有未报道的新作用，等离子体形成不由欧姆加热驱动。
中文摘要 AI 辅助
本实验研究了13.56 MHz的容性耦合等离子体，以确定在约10 W功率下、宽压力范围（约5 - 600 mTorr）内的功率吸收机制。测量了等离子体参数的轴向分布，以及功率电极（PE）上的直流自偏压电压V_{DC}，由此确定直流鞘层电压降V_{s}。电子欧姆功率吸收的轴向分布显示，功率沉积在低密度区域最高，在高密度区域最低，这表明等离子体形成并非由欧姆加热驱动。将概率论证与密度峰的位置相关联，以确定各压力下的电离平均自由程（λ_{iz}）。还计算了在PE处直流鞘层电压降中获得的电子加速度和平均电子速度，以独立确定λ_{iz}，并将其与从密度分布计算得到的结果进行比较。除最低压力（约5 mTorr）存在显著偏差外，所有压力下的一致性都良好。电子鞘层渡越时间仅为射频周期的一小部分，这意味着加速电子将射频场视为叠加在直流鞘层压降V_{s}上的瞬时“瞬时值”。PE上的负自偏压使射频摆动不对称，使其在大部分周期内为负。由于射频在负半周加速电子，在正半周从电子获取能量，因此在稳态测量过程中，对多个射频周期取平均后，净功率会转移给电子。除了约5 mTorr时随机加热占主导外，更高压力下的射频场呈现出一种此前未被报道的新作用。
英文摘要
A 13.56 MHz, capacitively coupled plasma is investigated experimentally to determine the power absorption mechanism across a wide pressure range ({\approx} 5 - 600 mTorr) at {\approx} 10 W. Axial profiles of plasma parameters are measured along with V_{DC}, the DC self-bias voltage on the powered electrode (PE), from which the DC sheath voltage drop, V_{s} is determined. Axial profiles of electron ohmic power absorption reveal that power deposition is highest in low-density regions and lowest in high-density regions, indicating that plasma formation is not driven by Ohmic heating. Probability arguments were correlated with locations of the density peaks to determine the ionization mean free paths (λ_{iz}) at each pressure. Electron acceleration and average electron velocity acquired in the DC sheath voltage drop at PE were also calculated to determine λ_{iz} independently for comparing with those calculated from the density profiles. The agreement is good for all pressures, barring the lowest pressure ({\approx} 5 mTorr) for which there is significant deviation. The electron sheath transit times are a small fraction of the RF period, implying that the accelerated electrons experience the RF field as instantaneous "spot values" superimposed on V_{s}, the DC sheath drop. The negative self-bias on PE renders the RF swing asymmetric making it negative for most of the cycle. Since the RF accelerates electrons when it is negative and takes energy from them when it is positive, net power is transferred to the electrons during the course of steady-state measurements, averaged over many RF cycles. Except at {\approx} 5 mTorr where stochastic heating dominates, the RF field at higher pressures exhibits a novel role, not hitherto reported.
