Characterization of pulsed dc magnetron sputtering plasmas

Pulsed dc magnetron reactive sputtering of dielectrics provides a deposition process without arcing. The deposition process is usually carried out with pulsing frequencies in the range 10–350 kHz and duty cycles in the range 50–90%. The operating conditions are typically optimized empirically and are critically dependent on the properties of the pulsed plasma in the immediate vicinity of the magnetron. We show how a combination of time-resolved Langmuir probe measurements and time-resolved optical emission spectroscopy can be used to characterize the pulsed magnetron plasma and gain insights that can only be obtained conclusively by correlating the results obtained by both techniques. The pulsed dc sputtering of Al and Ti targets and the reactive sputtering of their oxides were used as examples in our experiments. Our experiments were carried out at total pressures in the range 0.4–1.3 Pa in either pure Ar ('metallic' mode) or in Ar–O₂ mixtures ('oxide' or 'reactive' mode) with mixing ratios from 1:1 to 1:4.