Plasma kinetics of Ar/O2 magnetron discharge by two-dimensional multifluid modeling

Multifluid two-dimensional model was developed to describe the plasma kinetics of the direct current Ar/O2 magnetron, coupling two modules: charged particles and neutrals. The first module deals with three positive ions—Ar+, O2+, and O+—and two negative species—e− and O−—treated by the moments of Boltzmann’s equation. The second one follows seven neutral species (Ar, O2, O, O3, and related metastables) by the multicomponent diffusion technique. The two modules are self-consistently coupled by the mass conservation and kinetic coefficients taking into account more than 100 volume reactions. The steady state is obtained when the overall convergence is achieved. Calculations for 10% O2 in Ar/O2 mixture at 2.67 and 4 Pa show that the oxygen excited species are mainly created by electron collisions in the negative glow of the discharge. Decreasing the pressure down to 0.67 Pa, the model reveals the nonlocal behavior of the reactive species. The density gradient of O2 ground state is reversed with respect to all gradients of the other reactive species, since the latter ones originate from the molecular ground state of oxygen. It is also found that the wall reactions drastically modify the space gradient of neutral reactive species, at least as much as the pressure, even if the discharge operates in compound mode.