Photonic superlattice multilayers for EUV lithography infrastructure

A numerical study of EUV Bragg mirrors with superstructures is presented. These modifications of the standard Mo/Si mirror are periodic superlattices as well as depth grading of the superlattice multilayers. The main results concern a narrowing of the normal incidence peak and all-angle reflection at 13.5 nm. Best results are obtained with a combination of superlattices with 4 and 5 superperiods and depth grading. The effect of the spectral width of the EUV source is also taken into account.