Investigation on charged particles in inductively coupled Ar/O2 plasmas: The role of Ar proportion

Abstract

In this paper, a 2D fluid model is built to reveal the inductively coupled Ar/O2 plasma behavior at 300 W, 30 mTorr, in the gas mixture of 95% Ar −5% O2 and 10% Ar −90% O2. The reliability of the model is first verified by comparing the calculated results with the experimental data, and the consistent results are obtained. Then, the spatial distributions of the charged species densities are investigated. As Ar fraction decreases, the maximum densities of charged particles shift toward the coil significantly, and the O2+ becomes the dominant positive ion at higher O2 fractions. The main reaction mechanisms are also discussed. It is concluded that the electrons are generated by the ionization of background gases, and the Ar+ ions are primarily formed by the ionization of Ar. However, the charge exchange processes account for the most production of O2+ and O+ ions at a high Ar fraction. The loss at the walls is the most important process to the consumption of positive ions. For the O− ions, they are first generated by the dissociative attachment of O2 at ground state, followed by the metastable state, and they are destroyed either by the ion–ion recombination with Ar+ ions or the detachment with O atoms as the Ar proportion varies. Finally, the effect of the ion–ion recombination reaction rate coefficients is discussed. The results indicate that rate coefficients of the recombination reactions have a significant influence on the positive ion densities when the Ar fractions are high.