Effect of Si barrier layers on the thermal stability of Al(1 wt.%Si)/Zr multilayers designed as EUV mirrors

To improve the thermal stability of Al/Zr multilayers, eighteen Al(1 wt.%Si)/Zr multilayers with different thickness(0.4 nm, 0.6 nm and 0.8 nm) of Si barrier layers were prepared by using the direct-current magnetron sputtering system. All the multilayers were annealed from 100 ℃ to 500 ℃ in a vacuum furnace for 1 h. To evaluate the effect of Si barrier layers on the thermal stability of Al/Zr system, the multilayers were characterized by grazing incidence X-ray reflectance(GIXR) and X-ray diffraction (XRD). From the alloy-interlayer model in the GIXR, the roughness of Al layer decreases with increasing thickness of Si barrier layers, while the roughness of Zr layer increases. Based on the XRD, the changing trends of crystal sizes of Al and Zr can explain the results in the GIXR. Comparing with the multilayers without Si barrier layers in the annealing process, the sample with Si barrier layer(0.6 nm) have better structural performance, of which the multilayers could have a stable structural performance above 300 ℃.