Freestanding multilayer films for application as phase retarders and spectral purity filters in the soft X-ray and EUV ranges

A technique for fabrication of freestanding multilayers which are able to be used as optical elements in the soft X-ray and EUV ranges is reported. Two types of transmission mode elements have been developed: phase retarders for the aims of soft X-ray polarimetry and thin film spectral filters. A variety of phase retarders on the base of Cr/Sc, Cr/C, V/B4C and W/B4C freestanding multilayers were designed for a spectral region of "water window" (lambda approximate to 2 - 4.5 nm). The possibility to yield the phase shift between s- and p-polarizations as high as 90 at equal transparencies of these polarizations of 0.4% was experimentally demonstrated with Cr/Sc phase retarder close to the Sc L-edge of absorption (lambda = 3.11 nm). The set of freestanding absorption filters Cr/Sc, Mo/C, Zr/Si, Zr/Al with spectral windows within 2.2 to 22 nm wavelength range was developed for the aims of hot plasma diagnostics. We also fabricated Al/Si structures with supported mesh, which are transparent in the range lambda = 17 - 60 nm, for application in the sun astronomy. The sample of 160 mm in diameter Mo/ZrSi2 spectral purity filters with transparency of 70% (lambda = 13 nm) was fabricated as the probable component part of industrial EUV lithography tool. The preliminary testing of heat load withstandability was fulfilled for a number of freestanding multilayers consisting of Si, Zr, Mo and silicides of both metals. It was found that Mo/ZrSi2 structure is the challenge to withstand intensive heating up to 800 - 850 degrees C.