Characteristics of time modulated surface wave argon plasma

The behavior of argon plasma generated by a pulse-modulated surface-wave po wer with an Okamoto cavity was investigated using a time-resolved spectrome ter and a Lagmuir probe. Microwave power (2.45 GHz, similar to1 kW) was mod ulated by a square wave pulse with duration 10-100 mus and 10-80% duty rati o. Time resolved emission spectra of Ar I(811.5 nm, upper state energy E-u = 13.1 eV) and Ar I(419.8 and 355.4 nm, E-u = 14.6 and 15.0 eV, respectivel y) were obtained as a function of the duty ratio, power and pressure and co mpared with the probe signals. In the case of Ar I(419.8 and 355.4 nm), the intensity was increased rapidly (spike) just after the microwave power was turned on and just after the power turned off the intensity decayed rapidl y. On the other hand, no spike was observed for Ar I(811.5 nm) over the wid e pulse range and the intensity decayed more slowly just after the power tu rned off. The time evolutions of these signals are compared with the time v ariations of the floating potential (proportional to the electron temperatu re) and the ion saturation current (electron density) measured by the probe . Good correlation's were obtained between these results. The emission inte nsity ratio of these lines has a maximum with respect to the duty ratio for constant peak power. The time averaged ion current density and its radial distribution (uniformity) were improved compared with that of continuously driven plasma with the same time-averaged power. (C) 2001 Elsevier Science B.V. All rights reserved.