Impact of Mo Barrier Layers on the Interface and Microstructure of Al/Sc Multilayers for the Extreme Ultraviolet Range

Al/Sc multilayers are potential optical elements to be used for the extreme ultraviolet range at wavelengths longer than the Sc M_2,3 absorption edge. The existing research exhibits a significant gap concerning the incorporation of a barrier layer within the Al/Sc multilayer to enhance interface quality. A series of Al/Sc, Al/Sc/Mo, Al/Mo/Sc, and Al/Mo/Sc/Mo multilayers were fabricated by the direct-current magnetron sputtering technique. Grazing incidence X-ray reflectivity, transmission electron microscopy, selected area electron diffraction, energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray absorption spectroscopy were used to investigate the effect of Mo barrier layers on interface properties and layer microstructure of Al/Sc multilayers. The results indicate that Mo barrier layers with a thickness of approximately 0.5 nm at different interfaces perform different functions. The Mo barriers at Al-on-Sc interfaces primarily play a role in suppressing the columnar crystallization of Al layers, contributing to the smoothening of interfacial roughness. The thin Mo layers at Sc-on-Al interfaces mainly act as antidiffusion barriers, preventing the diffusion of Al atoms into Sc layers. A model of the impact of Mo barrier layers on the interface diffusion and microstructure of Al/Sc multilayers has been established.