Two-Dimensional Distributions of Ti and Ti+ Densities in High-Pressure Magnetron Sputtering Discharges

We measured two-dimensional distributions of Ti and Ti+ densities in magnetron sputtering plasmas by laser-induced fluorescence (LIF) imaging spectroscopy. It has been found that the production of Ti+ is enhanced by a high gas pressure. The peak of the Ti+ density is located at a distance of 4–5 cm from the target surface, indicating the gas-phase production of Ti+ in the downstream plasma. Since the plasma density and the electron temperature measured using a Langmuir probe are low in the downstream plasma, this result suggests that the dominant production process of Ti+ is not electron impact ionization of Ti (Ti+e→Ti+e+e). Although another candidate for the gas-phase production of Ti+ is Penning ionization (Ti+ArM→Ti++Ar+e), experimental results on ArM is negative about the contribution of Penning ionization to the gas-phase production of Ti+.