US Patent 11762278 Multilayer extreme ultraviolet reflectors

Extreme ultraviolet (EUV) mask blanks, production systems therefor, and methods of reducing roughness are disclosed. The EUV mask blanks comprise a multilayer reflective stack on a substrate comprising a plurality of pairs of alternating layers comprising a first layer and a second layer, the first layer including a first element selected from the group consisting of Si, B, Al, Mg, Zr, Ba, Nb, Ti, Gd, Y, and Ca; and the second layer including a second element selected from the group consisting of Ru, Mo, Ta, Sb, Tc, Nb, Ir, Pt, and Pd. Some EUV mask blanks described herein include interface layer between the first layer and the second layer, the interface layer including an interface element selected from the group consisting of Si, B, C, Al, Mo, and Ru.