Reflection Passband Broadening by Aperiodic Designs of EUV/Soft X-ray Multilayers

摘要

By using three conventional optimization algorithms, we have developed computer programs of layer thickness designing for reflection passband broadening of EUV/soft X-ray multilayers. Three programs with optimization by Simplex, quasi-Newton and Gradient methods were found to be effective to search for aperiodic Mo/Si multilayers of a leveled reflectance of 35% within a wavelength region between 13 nm and 15 nm, though the thickness structures were considerably different. For much shorter wavelengths in the water window, solutions of Cr/Sc multilayers were also found for a leveled 30% reflectance between 3.14 nm and 3.16 nm, and also for a 15% reflectance between 3.13 nm and 3.17 nm. The bandwidth / of these designs were improved from 286 of periodic multilayer to 137 and 66, respectively. Two practical design solutions were used to fabricate aperiodic Mo/Si multilayer mirrors by our ion beam sputtering system. The samples show EUV reflectance of more than 15% between 13 nm and 15 nm.