Characteristics of time modulated surface wave argon plasma

The behavior of argon plasma generated by a pulse-modulated surface-wave power with an Okamoto cavity was investigated using a time-resolved spectrometer and a Lagmuir probe. Microwave power (2.45 GHz, 1 kW) was modulated by a square wave pulse with duration 10±100 ms and 10±80% duty ratio. Time resolved emission spectra of Ar I(811.5 nm, upper state energy Eu ˆ 13:1 eV) and Ar I(419.8 and 355.4 nm, Eu ˆ 14:6 and l5.0 eV, respectively) were obtained as a function of the duty ratio, power and pressure and compared 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 rapidly. On the other hand, no spike was observed for Ar I(811.5 nm) over the wide pulse range and the intensity decayed more slowly just after the power turned off. The time evolutions of these signals are compared with the time variations of the ¯oating potential (proportional to the electron temperature) and the ion saturation current (electron density) measured by the probe. Good correlationʹs were obtained between these results. The emission intensity 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. # 2001 Elsevier Science B.V. All rights reserved