Experimental investigations of pulse-power-modulated inductive discharges

Abstract

Time-resolved probe measurements are carried out using the boxcar measurement method in a pulsed, low-pressure inductively coupled plasma. The characteristics of the transient behavior of the electron energy distribution function. (EEDF) and of the plasma parameters such as the electron density, the electron temperature, and the plasma and floating potentials, arc presented and analyzed with the global model of a, pulsed discharge. From the relaxation behavior of the EEDF and the analysis of the characteristic relaxation times of the electron density and temperature, the initial fast relaxation of high-energy electrons just after the power is turned off is found to be dominated by electron-atom inelastic collisions rather than the diffusive cooling effect at low pressure. A revised global model in which the effect of electron-atom inelastic collisions is included is presented. After the power is turned on, an initial very sharp rise in electron temperature followed by a decay of electron temperature is observed, and the peak electron temperature is found to increase with reducing duty cycle of the power pulse. A comparison of the measured EEDFs shows that the increase in the peak electron temperature under a, shorter duty cycle pulse is caused by the depopulation of low-energy electrons, not by the overpopulation of high-energy electrons.