The influence of background pressure on microstructure and chemical state of WC/SiC multilayers prepared by magnetron sputtering

WC/SiC multilayers are considered as promising optical elements for the application of reflecting hard X-rays efficiently, which allow for very small d-spacings owing to smooth and sharp interfaces. In this paper, to explore the influence of background pressure during fabrication, a set of WC/SiC multilayers with a period thickness of approximately 3 nm were prepared by direct current magnetron sputtering technique under different background pressures. The effect of residual background gases on the interface and surface morphology was investigated by using grazing incidence X-ray reflectivity, X-ray diffuse scattering, optical profiler, and atomic force microscope. High background pressure contributes to increased interface roughness, intensified interface diffusion, reduced lateral correlation length, and diminished vertical correlation. An increased root-mean-square surface roughness in high spatial frequency range is observed in case of high background pressure. The evolution of elemental distribution and chemical state in WC/SiC multilayers induced by varied background pressure was characterized by using X-ray photoelectron spectroscopy. According to the results, a mechanism by which background pressure influences the structural properties of WC/SiC multilayers has been established. Finally, it is concluded that to fabricate WC/SiC multilayers with favorable performance, the background pressure requires not exceeding 2 × 10⁻⁴ Pa.