A global (volume averaged) model of a Cl2/Ar discharge: II. Pulsed power modulation

Abstract

A global (volume averaged) model of a time-modulated Cl2/Ar discharge is developed and applied to investigate the temporal evolution and dependence of plasma parameters on the modulation frequency, duty ratio and argon content. The model is compared with and shown to be in acceptable agreement with measurements found in the literature in pure Cl2 pulsed discharges. We demonstrated that the electronegativity and the Cl+ and Cl to positive ion flux ratios can be controlled by modulating the power to the discharge and varying the argon content. The influence of argon dilution is mostly independent of the frequency and the duty ratio, being similar to that of the continuous power Cl2/Ar discharge. The time-averaged electronegativity n−/ne versus duty ratio peaks at about 8% duty ratio and 10 kHz frequency, being 20 times larger than in the continuous power discharge. The time-averaged Cl+ to positive ion flux is even larger than in the continuous power discharge, in particular at low frequencies and low duty ratios. The time-averaged ratio of Cl to positive ion flux has a minimum versus frequency at around 50 kHz and a maximum versus duty ratio at about 10–20% duty ratio. We believe these results indicate that the improved etching characteristics of pulsed Cl2 discharges that have been reported in the literature are a result of the increased Cl to positive ion flux ratio when the power is pulsed with a 10 kHz frequency and a moderately large duty ratio.