Exploring the impedance characteristics in an inverted radio-frequency capacitively coupled plasma discharge due to intense boundary emission

Abstract

Electron emission from boundaries is ubiquitous in radio-frequency capacitively coupled plasmas (RF-CCPs) and can exert a significant influence on discharge characteristics. In this work, particle-in-cell Monte-Carlo collisions (PIC-MCC) simulations with an external circuit are performed to investigate a conduction-current-dominated RF-CCP mode, termed the inverted RF-CCP, which is induced by strong boundary electron emission. In this mode, the displacement current becomes negligible, and the conduction current dominates in both bulk plasma and sheaths, as opposed to the classic RF-CCPs. The inverted RF-CCP also features weak resistive sheaths, and the plasma impedance is dominated by a resistive–inductive bulk region due to sheath inversion. Parametric scan of neutral pressure reveals the origin of the observed phase behavior. These findings provide practical methods for diagnosing the inverted RF-CCP, based on its distinctive impedance signature without direct sheath diagnostics. Additionally, we show that unbalanced electron emission can generate discharge asymmetry, enabling a unidirectional ion flow between electrodes.