A study of the oxygen dynamics in a reactive Ar/O₂ high power impulse magnetron sputtering discharge using an ionization region model

The oxygen dynamics in a reactive Ar/O₂ high power impulse magnetron sputtering discharge has been studied using a new reactive ionization region model. The aim has been to identify the dominating physical and chemical reactions in the plasma and on the surfaces of the reactor affecting the oxygen plasma chemistry. We explore the temporal evolution of the density of the ground state oxygen molecule $O 2 ( X 1 Σ g − )$⁠, the singlet metastable oxygen molecules $O 2 ( a 1 Δ g )$ and $O 2 ( b 1 Σ g )$⁠, the oxygen atom in the ground state O(³P), the metastable oxygen atom O(¹D), the positive ions $O 2 +$ and O⁺, and the negative ion O⁻. We furthermore investigate the reaction rates for the gain and loss of these species. The density of atomic oxygen increases significantly as we move from the metal mode to the transition mode, and finally into the compound (poisoned) mode. The main gain rate responsible for the increase is sputtering of atomic oxygen from the oxidized target. Both in the poisoned mode and in the transition mode, sputtering makes up more than 80% of the total gain rate for atomic oxygen. We also investigate the possibility of depositing stoichiometric TiO₂ in the transition mode.