REACTIVE ALTERNATING-CURRENT MAGNETRON SPUTTERING OF DIELECTRIC LAYERS

Dielectric layers like Al2O3, SiO2, and Si3N4 have been produced by a reactive ac magnetron sputtering process, using a two cathode arrangement. Within a frequency range between 10 and 100 kHz, where the ions still completely follow the ac field, deposition rates comparable to the dc case could be achieved. In contrast to dc sputtering above a certain frequency of some ten kHz no disturbing charges on dielectric parts of the target surface can build up, thus preventing the well-known problem of arcing. Above this frequency the probability of arcing decreases to zero, leading to a stable process. High deposition rates of about 40 angstrom/s could be realized for the Al- and Si-based reactive processes. This was achieved by a control unit combining the discharge voltage and the reactive gas flow in order to stabilize the transition between the metallic and the dielectric sputter mode. In case of dynamic deposition a homogeneous film thickness distribution on a substrate area of 350 X 450 mm2 of better than +/- 5 % was obtained. An easy scale-up to bigger cathodes is expected due to the simple coupling of the ac power to the cathodes in this frequency range. The investigated dielectric layers are characterized by optical and mechanical measurements.