Optical performance, structure and thermal stability of Al(1wt.-%Si)/Zr and Al(pure)/Zr multilayers designed for the 17–19 nm range

We report on the optical performance, structure and thermal stability of periodic multilayer films containing Zr and Al(1wt.-%Si) or Al(pure) layers designed for the use as extreme ultraviolet (EUV) high reflective mirrors in the range of 17–19 nm. The comparison of Al/Zr (Al(1wt.-%Si)/Zr and Al(pure)/Zr) multilayers fabricated by direct–current magnetron sputtering shows that the optical and structural performances of two systems have much difference because of Si doped in Al. From the results of grazing incidence X-ray reflection (GIXR), X-ray diffraction (XRD), and EUV, the Si can disfavor the crystallization of Al and smooth the interface, consequently increase the reflectance of EUV in the Al(1wt.-%Si)/Zr systems. For the thermal stability of two systems, the first significant structural changes appear at 250 oC. The interlayers are transformed from symmetrical to asymmetrical, where the Zr-on-Al interlayers are thicker than Al-on-Zr interlayers. At 295 oC for Al(pure)/Zr and 298 oC for Al(1wt.-%Si)/Zr, the interfaces consist of amorphous Al-Zr alloy transform to polycrystalline Al-Zr alloy which can decrease the surface roughness and smooth the interfaces. Above 300 oC, the interdiffusion becomes larger, which can enlarge the differences between Zr-on-Al and Al-on-Zr interlayers. Based on the analyses, the Si doped in Al cannot only influence the optical and structural performances of Al/Zr systems, but also impact the reaction temperatures in the annealing process.