Numerical simulation of inductively coupled Ar/O₂ plasma

Abstract

In the inductively coupled plasma (ICP) discharge, surface processes, such as reflection, de-excitation, and recombination, can occur when active species arrive at material surfaces, which accordingly influences the plasma properties. In this work, a fluid model is carried out to study the Ar/O<sub>2</sub> plasma generated by ICP reactors made of different materials. In simulation, sticking coefficient is employed to estimate the surface reactions on different materials. As the reactor material changes from stainless steel to anodized aluminum to copper, the sticking coefficient of surface reaction O → 1/2O<sub>2</sub> decreases. It is found that the reactor material has a great effect on species density. In the stainless steel reactor, the densities of O atoms at grounded and excited states are much lower because more O<sub>2</sub> molecules are generated from the surface reaction, and yielding a much higher density of O<sub>2</sub><sup>+</sup> which is mainly created from the ionization process of O<sub>2</sub>. Similarly, the high density of O<sub>2</sub> also enhances the production of O<sub>2</sub>(a<sup>1</sup>△<sub>g</sub>) molecules by the excitation process, and O<sup>-</sup> ions via the dissociation attachment reaction. On the contrary, more electrons are consumed via the collisions between electrons and O<sub>2</sub> or O<sub>2</sub><sup>+</sup>. Therefore, the electron density obtained in the copper reactor is highest. The densities of Ar<sup>+</sup> and Ar<sub>m</sub> also increase with the decreasing sticking coefficients. The densities of O<sup>+</sup> and O<sub>2</sub><sup>+</sup>ions peak below the coil in the stainless steel reactor, whereas the radial uniformities are improved in the copper reactor. In the three reactors, the electrons distribute evenly at the reactor center region. The O and O<sub>2</sub>(a<sup>1</sup>△<sub>g</sub>) densities present significant peaks below the coil, while the maxima of Ar+ and Arm densities are below the coil. As for O(<sup>1</sup>D), the maximum density below the coil region moves toward the reactor center as the reactor material changes from stainless steel to copper. Finally, the effect of sticking coefficient of O → 1/2O<sub>2</sub> is studied. The results show that the O density decreases with the sticking coefficient, but the opposite trend is observed in O<sub>2</sub> density. It is noticed that the sticking coefficient is found to have little effect on species densities when it is higher than 0.5.