Temporal evolution of plasma characteristics in synchronized dual-level RF pulsed capacitively coupled discharge

Plasma parameters (electron density, electron temperature and relative light intensity) often follow an unstable state at the initial pulse stage in pulsed radio frequency discharges. For instance, the electron temperature and the excitation rate often experience overshoot phenomena within a short time after the pulsed power is turned on, while the electron density first shows a sharp increase and then continues to increase more slowly before reaching a stable value within a relatively longer time. A systematic interpretation of the evolution of plasma parameters in synchronized dual-level radio frequency pulsing capacitively coupled plasmas is reported based on 1D3V particle-in-cell simulations with Monte Carlo Collisions in argon. The low electron density and rapid sheath expansion accompanied by a strong electric field in the bulk, are found to be of great importance for the overshoot of the electron temperature and excitation rate. In addition, a time-varying ambipolar electric field develops at the initial pulse stage, which compresses the plasma bulk toward the discharge center, contributing to a sharp increase of the plasma density.