BIAS FORMATION IN A PULSED RADIOFREQUENCY ARGON DISCHARGE

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 cou pled, rf argon plasma. In particular this article investigates the tim e-constants involved in the development and evolution of the bias volt age in asymmetric reactor geometry. Surprisingly, the charging time fo r the blocking capacitor does not occur on electron time scales, but i s influenced primarily by the ambipolar drift of ions to the earthed e lectrode. It is shown that following plasma breakdown there is a net c urrent 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 f low 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. c apacitor. From the simulation it can be seen that during this period t he plasma potential in the center of the discharge is higher than one would expect, preventing electrons from reaching the earthed electrode . (C) 1997 American Institute of Physics.