The thermal stability of Al(1%wtSi)/Zr EUV mirrors

Abstract

Six Al(1%wtSi)/Zr multilayers are deposited on Si substrates by using the direct-current magnetron sputtering system, and annealed from 100 °C to 500 °C temperature in a vacuum furnace for 1 h. To evaluate the thermal stability of Al(1%wtSi)/Zr multilayers, the multilayers were characterized by grazing incidence X-ray reflectance, X-ray diffraction, X-ray emission spectroscopy, and near-normal incident extreme ultraviolet (EUV) reflection. The symmetric and asymmetric interlayer models are used to present the interfacial structure before and after 300 °C. The Al(1%wtSi)/Zr multilayer annealed up to 200 °C maintains the initial symmetric multilayer structure, and keeps almost the similar EUV reflectivity as the nonannealed sample. From 300 °C, interdiffusion is much greater at the Zr/Al interface compared with the Al/Zr interface. And the interfacial phases of Al-Zr alloy transform from amorphous to polycrystalline, which induces the deterioration of multilayer structure and the decrease of EUV reflectivity. However, up to 500 °C, the polycrystalline Al-Zr compound does not destroy the multilayer completely.