Al/Zr multilayer mirror and its thermal stability for EUV application

Abstract

Two kinds of Al/Zr (Al(1%wtSi)/Zr and Al(Pure)/Zr) multilayers in the region of 17-19nm were deposited on fluorine doped tin oxide coated glass by using direct-current magnetron sputtering technology. Based on the fitting data of grazing incident X-ray reflection and near-normal incident (EUV) reflectance, the interfacial roughness in the Al(1%wtSi)/Zr is lower than that in Al(Pure)/Zr because of the presence of silicon in Al. For the further characterization of Al(1%wtSi)/Zr multilayers, six samples deposited on Si substrates were annealed from 100 °C to 500 °C temperature in a vacuum furnace for 1 h. Based on the results of EUV and X-ray diffraction, the Al(1%wtSi)/Zr multilayer has a stable structure up to 200 °C, and keeps almost the similar EUV reflectivity as the non-annealed sample. After 300 °C, the amorphous of Al-Zr alloy is transformed to polycrystalline in the interface, which could be the reason for the decrease of EUV reflectivity. The polycrystalline Al-Zr compound does not destroy the multilayer completely even up to 500 °C.