Zr/Mg multilayer mirror for extreme ultraviolet application and its thermal stability

Zr/Mg multilayer mirror was proposed for extreme ultraviolet (EUV) spectral range and deposited by magnetron sputtering. Its thermal stability during annealing up to 600 °C was evaluated by EUV reflection measurements, x-ray analyses, and transmission electron microscopy and found superior to that of Y2O3/Mg, SiC/Mg, and Co/Mg. The reflectance of as-deposited Zr/Mg multilayer is 30.6% at wavelength of 30.4 nm. The reflectance slightly decreases with annealing temperature when not above 500 °C and eventually drops to 15.1% at 600 °C. The degradation of performance is attributed to roughening induced by strain relaxation rather than interdiffusion or alloy compound formation.