Time-resolved optical emission spectroscopy of pulsed DC magnetron sputtering plasmas

Reactive magnetron sputtering of dielectrics using pulsed DC power in the frequency range between 5-350 kHz provides a deposition process without arcing. We studied the optical emission spectra of aluminium, argon and oxygen during the magnetron sputter deposition of Al in Ar and the reactive sputter deposition of Al₂O₃ in an Ar/O₂ gas mixture using a fast intensified CCD camera. Time-resolved as well as time-averaged optical emission spectroscopic studies were carried out. The time-resolved studies focused on the temporal behaviour of the various emissions during the decay of the plasma after the power is turned off. Decay times ranging from 1 to 4 νs were observed. A detailed analysis of the various processes that contribute to the emission of a particular emission line and its decay was carried out and an attempt was made to relate the various decay times to the dynamics of, respectively, the decay of the fast electrons, the Ar metastables, the Al atoms (metallic mode) and the O atoms (oxide mode).