Low-frequency modulation of pulsed dc or rf discharges for controlling the reactive magnetron sputtering process

Pulsed d.c. discharges (20-60 kHz) and r.f. discharges (13.56 Mhz) are known to prevent electric instabilities due to arcing when highly insulating compounds are deposited by reactive magnetron sputtering. This paper shows how a low-frequency modulation (1-10 Hz) of these discharges can overcome the difficulty due to the instability of the sputtering process itself with its associated hysteresis effect caused by the rapid transition between a clean target and a target poisoned by reaction products with the reactive gas. This new, simple and economical method does not need the use of a complex fast feedback control system of the reactive gas partial pressure. The application of this method will be particularly illustrated by the deposition of amorphous alumina films.