O− density measurements in the pulsed-DC reactive magnetron sputtering of titanium

The spatial structure of the O− density reveals a distinct peak 75 mm from the target close to but not at the position of the null in the magnetic field, falling by a factor of eight for increasing distances up to 30 mm both towards and away from the target. The highest O− density recorded at this position was 1 × 1016 m−3, at a time of 2.12 μs into the pulse. From a comparison between on- and off-phase densities and using an intuitive model of the plasma, the results indicate that most negative ions are created in the bulk plasma. The density of target-borne O− ions is estimated to be about 1 × 1015 m−3 varying little with position, possibly forming a beam-like structure.