Development of High-Reflection Mirrors of Fluoride Multilayers for F2 Excimer Laser by Ion Beam Sputtering Method

High-reflection mirrors of fluoride multilayers were developed for a F2 excimer laser, using the ion beam sputtering method. Fluoride multilayer mirrors deposited by ion beam sputtering method are known to have good morphology and low scattering loss, but it was rather difficult to reduce their absorption loss. In this work, the reflectance of the mirror composed of AlF3/LaF3 layers was improved to 93.6% at a wavelength of 157 nm with an incidence angle of 45° by the optimization of deposition conditions. This value of reflectance is almost equivalent to that of mirrors deposited by the conventional deposition method.