Time evolution of ion energy distributions and optical emission in pulsed inductively coupled radio frequency plasmas

Abstract

This article reports the results of time-resolved measurements of ion energy distributions (IEDs), relative ion densities, as well as optical emissions and electrical characteristics in pulsed inductively coupled plasmas for the simple gas mixture of oxygen and argon (50%Ar:50%O2). The peak radio frequency power, frequency, repetition rate, and duty cycle were 200 W, 13.56 MHz, 500 Hz, and 85%, respectively. Examination of the time evolution of the data over the pulse cycle indicates that when the plasma is energized, it begins in the dim (E) mode undergoing at first slow changes in certain plasma parameters. After about 1.2 ms, a sudden transition to the bright (H) mode occurs. The characteristics of the IEDs are consistent with an average plasma potential profile that has (a) a relatively large collisionless sheath and narrow presheath during the dim mode and (b) a very narrow sheath and greatly extended presheath during the bright mode; the ion mean free path influences the peak position of the IED during the bright mode. For most of the pulse cycle, the relative abundances of the ions Ar+, O2+, and O+ maintain the relation %O2+⩾%Ar+>%O+.