Characterization of Mo/Si soft X-ray multilayer mirrors by grazing-incidence small-angle X-ray scattering

The morphology of buried interfaces plays a key role in high performing Mo/Si soft X-ray mirrors. We show that grazing-incidence small-angle X-ray scattering is a highly effective and non-destructive diagnostic technique for analysis of buried interfaces. The parameters of average interface autocorrelation function can be determined unambiguously. Additionally period thickness, roughness of interfaces and an effective number of vertically correlated periods can be extracted. The multilayer mirrors were prepared by e-beam evaporation on heated and unheated substrates, ion beam assisted e-beam evaporation, ion beam sputtering and RF magnetron sputtering. The latter three techniques produce multilayer mirrors with comparable interface roughness. The differences in lateral correlation length and Hurst parameter are found.