Optical performance, structure and thermal stability of Al（lwt.-%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 con- taining Zr and Al（lwt.-%Si） or Al（pure） layers designed for the use as extreme ultraviolet （EUV） high reflective mirrors in the range of 1~19 am. The comparison of A1/Zr （Al（lwt.-%Si）/Zr and Al（pure）/Zr） multilayers fabricated by direct-current magnetron sputtering shows that the optical and structural per- formances of two systems have much difference because of Si doped in A1. From the results of grazing incidence X-ray reflection （GIXR）, X-ray diffraction （XRD）, and EUV, the Si can disfavor the crystalliza- tion of AI and smooth the interface, consequently increase the reflectance of EUV in the Al（lwt.-%Si）/Zr systems. For the thermal stability of two systems, the first significant structural changes appear at 250 ~C. The interlayers are transformed from symmetrical to asymmetrical, where the Zr-on-A1 interlayers are thicker than Al-on-Zr interlayers. At 295 ~C for Al（pure）/Zr and 298 ~C for Al（lwt.-%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 ~C, 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.