Nonlinear intermodulation and power coupling in low-pressure asymmetric dual-frequency capacitively coupled plasmas

Abstract Intermodulation of the current, voltage and dissipated power, resulting from the interaction between driving sources and the nonlinear plasma load, is a common phenomenon in dual-frequency capacitively coupled plasmas (DFCCPs). This phenomenon affects the sheath kinetics and significantly impacts power matching for specific discharge conditions. In this study, we investigate the intermodulation phenomenon in DFCCP discharges using a two-dimensional axisymmetric implicit electrostatic particle-in-cell/Monte Carlo collision (PIC/MCC) model that contains an external matching circuit. Simulation results demonstrate that the presence of intermodulation distortions and high-frequency oscillations, excited by the plasma series resonance (PSR) effect, lead to the generation of a complex frequency spectrum. This spectrum includes DC, fundamental and harmonic components at low and high frequencies, as well as their sum and difference frequencies. Additionally, the simulation reveals that the low-frequency (LF) bias voltage influences the plasma impedance characteristics by modulating the sheath width, thereby altering the power transfer efficiency of the high-frequency source. At higher LF voltages, the plasma impedance exhibits significant cyclic variations, preventing effective power matching solely through matching network parameter optimization under constant voltage or constant power conditions. These findings enhance the understanding of the interactions between the plasma and external circuits and provide valuable insights for impedance-matching design in industrial applications.