Pulsed dc self-sustained magnetron sputtering

The magnetron sputtering has become one of the commonly used techniques for industrial deposition of thin films and coatings due to its simplicity and reliability. At standard magnetron sputtering conditions (argon pressure of $∼0.5Pa$⁠) inert gas particles (necessary to sustain discharge) are often entrapped in the deposited films. Inert gas contamination can be eliminated during the self-sustained magnetron sputtering (SSS) process, where the presence of the inert gas is not a necessary requirement. Moreover the SSS process that is possible due to the high degree of ionization of the sputtered material also gives a unique condition during the transport of sputtered particles to the substrate. So far it has been shown that the self-sustained mode of magnetron operation can be obtained using dc powering (dc-SSS) only. The main disadvantage of the dc-SSS process is its instability related to random arc formation. In such case the discharge has to be temporarily extinguished to prevent damaging both the magnetron source and power supply. The authors postulate that pulsed powering could protect the SSS process against arcs, similarly to reactive pulsed magnetron deposition processes of insulating thin films. To put this concept into practice, (i) the high enough plasma density has to be achieved and (ii) the type of pulsed powering has to be chosen taking plasma dynamics into account. In this article results of pulsed dc self-sustained magnetron sputtering (pulsed dc-SSS) are presented. The planar magnetron equipped with a $50mm$ diameter and $6mm$ thick copper target was used during the experiments. The maximum target power was about $11kW$⁠, which corresponded to the target power density of $∼560W∕cm2$⁠. The magnetron operation was investigated as a function of pulse frequency $(20–100kHz)$ and pulse duty factor (50%–90%). The discharge (argon) extinction pressure level was determined for these conditions. The plasma emission spectra (⁠$400–410nm$ range) and deposition rates were observed for both dc and pulsed dc self-sustained sputtering processes. The pulse characteristics of the voltage and current of the magnetron source during pulsed dc-SSS operation are shown. The presented results illustrate that a stable pulsed dc-SSS process can be obtained at a pulsing frequency in the range of $60–90kHz$ and duty factor of 80%–90%.