Characterization of pulse-modulated inductively coupled plasmas in argon and chlorine

The characteristics of pulse-modulated inductively coupled plasmas in argon and chlorine have been experimentally investigated. Measurements were performed for peak rf powers between 150 and 400 W at 13.56 MHz, duty cycles between 10 and 70%, and pulse repetition frequencies between 3 and 20 kHz. Over this parameter space, measurements were performed of the time dependent forward and reflected rf powers into the matching network, coil voltage, rf variation of the plasma potential, electron density, and Cl- density. These measurements indicated that for the first 5-30 rf cycles of each pulse, the discharges probably were operating in a capacitively coupled discharge mode with rf variations in the plasma potential of several hundreds of volts and relatively low electron density. Measurements of the electron density in pulse-modulated chlorine discharges indicated that the plateau electron density was a function of the duty cycle; the plateau electron density was lower for higher duty cycles. This may indicate that the ratio of Cl to Cl-2 was changing with duty cycle. In addition, a microwave radiometer was used to provide an indication of the time-dependent electron temperature. Large spikes in the microwave radiation temperature were noted at the turn-on of the rf power pulses and, in some cases, at the transition from a capacitively coupled to an inductively coupled plasma. (C) 1997 American Institute of Physics.