The existence of a double S-shaped process curve during reactive magnetron sputtering

The four dimensional parameter space (discharge voltage and current and reactive gas flow and pressure) related to a reactive Ar/O2 DC magnetron discharge with an aluminum target and constant pumping speed was acquired by measuring current-voltage characteristics at different oxygen flows. The projection onto the pressure-flow plane allows us to study the well-known S-shaped process curve. This experimental procedure guarantees no time dependent effects on the result. The obtained process curve appears not to be unique but rather two significantly different S-shaped curves are noticed which depend on the history of the steady state target condition. As such, this result has not only an important impact on the fundamental description of the reactive sputtering process but it can also have its consequences on typical feedback control systems for the operation in the transition regime of the hysteresis during reactive magnetron sputtering