A method for measuring individual ion density in an Ar/He mixture inductively coupled plasma

Abstract

A method for measuring individual ion density and for measuring radial distribution is developed in an argon/helium mixture inductively coupled plasma using the floating harmonic method (FHM) and the electron energy probability function (EEPF) measurement. In order to measure the ion density, the ion saturation current is measured using the FHM, and the electron temperature and electron density are obtained from the EEPF measurement. In addition, plasma quasi-neutrality, ion acoustic wave dispersion relation, and ion saturation current formula are used to obtain the ion density. Ion density is compared for the case of using the common Bohm velocity and for the case of using the individual Bohm velocity. Under various conditions, increasing power results in higher density of both argon and helium ion, while argon ion density increase and helium ion density decreases with pressure. With increasing argon ratio and pressure, electron density increases, but electron temperature deceases. Consequently, fewer electrons are available to ionize He, leading to a reduction in helium ion density. The measured radial distributions of argon and helium ion at 5 mTorr reveal that the argon ion distribution exhibits a center-high distribution, whereas the helium ion distribution is relatively uniform.