An estimate of the potentials developed on coated anodes during pulsed DC reactive sputtering

摘要

Pulsed dc power supplies and switching circuits that priodically ground or positively bias cathodes are new widely used to reduce arciing in reactive sputtering. A number of authors have estimated the potentials developed on posioned targets and the conditions that lead to successful arc suppresion. It is also recognized that insulating layers deposited on grounded surfaces play an important role in pulsed reactive sputtering processes as well. However, this "disappearing anode" effect has not received similar anlaytical treatment. We present a calculation of the potentials that can develop on insulating films, deposited during the coating process, when the currents to ground capacitively coule through them. Each sputter/discharge cycle, typically lasting tens of microseconds, is treated as two separate quasi-dc events. An analytical expression is derived relating the surface potential to the effective anode size and sputtering parameters. Equilibrium values of negative 100 volts or more with respect to ground are possible in representative cases. The fields produced by these potentials are sufficient to casue electrical breakdown in the coatings that can be an important source of defects and contamination in some applications.