Impedance matching design for capacitively coupled plasmas considering coaxial cables

Abstract

Capacitively coupled plasmas (CCPs) are widely used in plasma processing applications, where efficient power coupling between the radio frequency (RF) source and the plasma is crucial. In practical CCP systems, impedance matching networks (IMNs) are employed to minimize power reflection. However, the presence of coaxial cables can significantly impact plasma impedance and matching performance. We develop a comprehensive simulation framework for the IMN design of CCPs, fully considering the effects of RF coaxial cables. The model self-consistently couples a distributed transmission line (TL) model, a lumped-element circuit model, and an electrostatic particle-in-cell model. This coupled model is used to investigate the impact of coaxial cables on matching performance under various discharge conditions and cable configurations. The simulation results indicate that the optimal power transmission efficiency was achieved after 6 matching iterations. The power coupled to the CCP increased from 2.7 W before matching to 180.9 W, and the reflection coefficient ultimately decreased to 0.003. The results also reveal that neglecting the cables will lead to a decrease in the power dissipated in the CCP. The proposed method demonstrates effectiveness in achieving impedance matching for different gas pressures (75–300 mTorr) and cable lengths. It can be concluded that the matching speed is faster for an appropriate cable length. This work provides valuable insights into the role of TLs in CCP impedance matching and offers a practical tool for optimizing power delivery in realistic CCP systems with RF coaxial cables.