Bias formation in a pulsed radiofrequency argon discharge

Abstract

A one dimensional (1D) particle-in-cell (PIC) computer simulation has been used in conjunction with a small experimental plasma reactor, to investigate the effects of pulsing on a low pressure, capacitively coupled, rf argon plasma. In particular this article investigates the time-constants involved in the development and evolution of the bias voltage in asymmetric reactor geometry. Surprisingly, the charging time for the blocking capacitor does not occur on electron time scales, but is influenced primarily by the ambipolar drift of ions to the earthed electrode. It is shown that following plasma breakdown there is a net current flow in the system which charges the blocking capacitor in the external matching circuit and produces the bias voltage. Both the PIC simulation and the experimental measurements show that a net current flow is produced by a delay in the onset of the electron current to the earthed electrode, which is correlated to the charging time of the capacitor. From the simulation it can be seen that during this period the plasma potential in the center of the discharge is higher than one would expect, preventing electrons from reaching the earthed electrode.