Stress, reflectance, and stability of Ru/Be multilayer coatings with Mo interlayers near the 11 nm wavelength

The stress, reflectance, and temporal stability of Ru/Be multilayer mirrors, both with and without Mo interlayers, were studied. A Ru/Be MLM was found to have zero stress at a Ru layer thickness-to-period ratio of γ ∼ 0.4. By adding Mo interlayers to both interfaces, it is possible to achieve a record-high reflectance (R > 71%) at a wavelength close to 11 nm while maintaining near-zero stress levels. A Ru/Be MLM with Mo interlayers at both interfaces also demonstrates high temporal reflectance stability. Ru/Be MLMs may be of interest for the next-generation projection lithography at a wavelength of 11.2 nm.