Discharge properties of helicon oxygen plasma in the source and expansion chambers

Abstract

In this paper, a study of a helicon discharge with O2 gas, operating at 13.56 MHz frequency and powers between 0–1500 W and pressure between 3 × 10−3 and 8 × 10−3 mbar is presented. Measurements of plasma parameters were made in the plasma production chamber as well as in the downstream expansion chamber. In the source chamber, transition from E to H and finally to W mode appears by increasing the input radio frequency (RF) power. To the best of our knowledge, this is the first detailed report of Helicon mode transition in Oxygen discharge. Mode transition is further confirmed by studying the radial density profile and by external matching circuit parameters measurement. Comparison of Langmuir probe I-V measurements and electron energy distribution function (EEDF) in source and expansion chambers confirms formation of negative ions. Negative ion fraction is measured in the expansion chamber by using two-probe method and densities of charged particles (electrons, positive and negative ions) are calculated using standard Langmuir probe theory and quasi-neutrality condition.