Self-consistent particle-in-cell/Monte Carlo simulation of RF magnetron discharges of oxygen/argon mixture: effects of partial pressure ratio

The characteristics of RF planar magnetron discharges of O₂/Ar mixture are clarified using the particle-in-cell/Monte Carlo method. The simulation is carried out for axisymmetrical magnetic fields. The spatial and temporal behavior of magnetron discharge is examined in detail. The O^- ions are trapped in the plasma bulk by the time-averaged potential. The O^- density is governed by a balance of generation and loss of O^-. The positive ions Ar⁺, O₂⁺, and O⁺ are distributed in such a way that the charge neutrality is kept in the plasma bulk. Since the peak point of O^- density does not coincide with that of electron density, the spatial distributions of Ar⁺, O₂⁺, and O⁺ have two peaks. The number densities of Ar⁺ and O^- ions drastically increase when oxygen is added to the discharge gas Ar, and then saturated. In the case when the mole fraction of oxygen increases, the self-bias voltage on the target decreases. This phenomenon is investigated in detail and a clear physical explanation is presented.