Experimental and simulation studies of E-H mode transitions in Cl2 inductively coupled plasmas

In this study, a diagnostic investigation of plasma density and neutral gas temperature during mode transition in radio frequency (RF) inductively coupled Cl2 plasma is conducted using cutoff probes and fiber Bragg grating. A coupled electromagnetic and global model is used to analyze the underlying physical mechanisms. Results show that the threshold coil current for E–H transition increases with pressure (10–80 mTorr), accompanied by enhanced hysteresis. Hysteresis is also observed in the coil current response to RF power, with opposite trends exhibited during increasing and decreasing power near the mode transition. Capacitive coupling dominates at low plasma densities, while inductive coupling predominates at higher densities. The magnitudes of capacitive and inductive power are separately calculated to quantify their respective contributions during the mode transition, using an analytical electromagnetic model. It is indicated that the dominance alternates between capacitive and inductive coupling mechanisms as the electron density varies and that the mode transition occurs when their contributions become comparable. The distinct gas heating mechanisms in E- and H-modes account for the observed differences in neutral gas temperature. Experimental and simulation results both indicate significantly different power coupling efficiencies between the two modes. Notably, hysteresis emerges in simulations only when the actual gas temperature is considered. Simulations reveal that elevated neutral gas temperatures reduce the power required to sustain H-mode, suggesting that gas heating contributes to hysteresis behavior.