Increase of Ar⁺ ion density in argon RF magnetron discharges caused by the addition of a small amount of oxygen

Particle-in-cell/Monte Carlo (PIC/MC) simulations were performed for radio frequency (RF) planar magnetron discharges of pure argon gas and an O₂-Ar gas mixture. The number densities of Ar⁺ and O^- ions drastically increased when oxygen was added to the Ar discharge gas. Moreover, the spatial distributions of positive ions, Ar⁺, O₂⁺, and O⁺, had two peaks in the O₂/Ar mixture discharge. The positive ions were distributed in such a way that the charge neutrality was kept in the plasma bulk, indicating that the behavior of Ar⁺ ions is influenced by the existence of O^-ions. The mechanism of this phenomenon is herein clearly explained by visualizing results of the simulation.