Power dissipation during the ignition of pulse-modulated dual RF capacitively coupled argon plasmas at different pressures

Shi, De-Hua and Wang, Xiao-Kun and Zhao, Kai and Donkó, Zoltán and Schulze, Julian and Liu, Yong-Xin (2025) Power dissipation during the ignition of pulse-modulated dual RF capacitively coupled argon plasmas at different pressures. PLASMA SOURCES SCIENCE AND TECHNOLOGY, 34. No. 055016. ISSN 0963-0252 (print); 1361-6595 (online)

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Abstract

The power absorption mechanisms of charged particles during the ignition of pulsed dual radio-frequency (12.5 MHz/2.5 MHz) capacitively coupled argon plasmas at different gas pressures are investigated by multi-fold experimental diagnostics and particle-in-cell/Monte Carlo collision (PIC/MCC) simulations. All the experimental results, including the evolution of the macroscopic plasma and electrical parameters, and the spatiotemporal distribution of the electron-impact excitation rate during the ignition process are well reproduced by the PIC/MCC simulations. It is found that by increasing the pressure, the plasma ignition occurs more rapidly and meanwhile the RF power dissipation is significantly enhanced during the ignition phase. At the beginning of the ignition phase electrons dissipate energy rapidly via ionization and excitation, leading to an overshoot of the optical emission intensity (OEI) and the RF power dissipation, while the ion energy absorption rate is relatively low and grows slowly. When the OEI and the RF power deposition overshoot, the charge density increases and accordingly the electron and especially the ion power absorption rate is enhanced due to an enhanced electric field within the space charge regions near the electrodes. During the post-ignition phase the sheaths form and the energy dissipated to the ions surpasses that dissipated to the electrons. At low pressure, e.g. 30 Pa, the electron power absorption mainly occurs inside the bulk region and the electron excitation and ionization dynamics resemble each other. By contrast, at higher pressure, e.g. 60 Pa and 120 Pa, the excitation and ionization dynamics behave differently, i.e. the excitation is mainly produced by high-energy electrons generated due to the expanding sheath and the drift electric fields inside the bulk region, while the ionization generated by γ-electrons is mainly located at the edge of the fully expanded sheaths.

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