Perspective: Is there a hysteresis during reactive High Power Impulse Magnetron Sputtering (R-HiPIMS)?

This paper discusses a few mechanisms that can assist to answer the title question. The initial approach is to use an established model for DC magnetron sputter deposition, i.e., RSD2013. Based on this model, the impact on the hysteresis behaviour of some typical HiPIMS conditions is investigated. From this first study, it becomes clear that the probability to observe hysteresis is much lower as compared to DC magnetron sputtering. The high current pulses cannot explain the hysteresis reduction. Total pressure and material choice make the abrupt changes less pronounced, but the implantation of ionized metal atoms that return to the target seems to be the major cause. To further substantiate these results, the analytical reactive sputtering model is coupled with a published global plasma model. The effect of metal ion implantation is confirmed. Another suggested mechanism, i.e., gas rarefaction, can be ruled out to explain the hysteresis reduction. But perhaps the major conclusion is that at present, there are too little experimental data available to make fully sound conclusions

Sputter deposition of porous thin films from metal/NaCl powder targets

A method to deposit porous thin films is elucidated. For this purpose, NaCl powder was mixed with a metal powder, cold pressed, and used as a target material in order to deposit a metal/NaCl thin film by DC magnetron sputtering. The thin film was immersed in water after deposition to remove the salt and to obtain a porous film. The low thermal conductivity of the target results in target heating and salt sublimation. In this way, the salt content in the layer and hence the film porosity are controlled by the discharge power. This procedure was carried out for Cu and Ti. The study focuses on the deposition of porous Cu thin films. From scanning transmission electron microscopy images, two film structures were observed. Films with a density higher than approximate to 40% of the bulk density exhibit a homogeneous spongelike microstructure with pores around 20nm. At lower density, a noncontinuous, fractured layer is formed. The blocks between the observed cracks manifest itself in the form of columnar pores. The lowest measured density was approximate to 23% of the bulk density. This approach combines the flexibility of powder targets and the scalability of magnetron sputtering and avoids the usage of aggressive chemicals

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