On the origin of multilayered structure of W-B-C coatings prepared by non-reactive magnetron sputtering from a single segmented target

Abstract

Multilayered coatings are routinely obtained in non-reactive processes employing multiple sources or in processes with a reactive gas. W-B-C coatings were sputter deposited in an industrial sputtering system in a non-reactive atmosphere onto substrates performing one- and two-axis rotations around a central cylindrical target composed of boron-carbide, tungsten and graphite ring-shaped segments. This study describes the unexpected multilayered structure of W-B-C coatings deposited by even the non-reactive sputtering of a single target. This multilayered structure exhibits a modulation of the chemical composition. While the tungsten content in a layer decreases, the amount of boron and carbon rises. The modulation period corresponds with the calculated thickness increment per one sample revolution around the central cathode. Experiments proved that the chemical composition of a coating and its deposition rate are very sensitive to the substrate position in the chamber. This was attributed to the different transport pathways of heavy (W) and light (C and B) atoms sputtered from the same target, but differently scattered by the working argon gas.