EUV multilayer mirror with suppressed reflectivity for CO2 laser radiation

We have developed a multilayer mirror for extreme ultraviolet (EUV) radiation (13.5 nm) which has near-zero reflectance for IR line radiation (10.6 mm). The EUV reflecting part is based on alternating B4C and Si layers. Substantial transparency of these materials with respect to the infrared radiation allowed integrating the multilayer coating in a Fabry-Perot etalon structure with a high loss factor for 10.6 mm. Samples were manufactured using magnetron sputtering deposition technique and demonstrated suppression of the CO2 laser radiation by up to 3 orders of magnitude. The EUV peak reflectance amounts 45% at 13.5 nm, with a bandwidth at FWHM being 0.284 nm. Therefore such a mirror could replace conventional multilayer mirrors to suppress undesired spectral components in monochromatic imaging applications, including EUV photolithography.