Characteristics of optical components for soft x-ray microscopy and x-ray holography using an undulator radiation optical system (abstract)

Abstract

X-ray Fresnel zone plates and transmission gratings, have been fabricated using fine-focused electron-beam lithography and Ta-on-SiN x-ray mask fabrication technique. The optical components for x-ray microscopy and x-ray holography were evaluated in an undulator radiation system. Nanometer lithography using fine-focused electron-beam writing machines is now regarded as an important technology to create new devices on very small structures such as quantum wires or boxes and new scientific probe elements such as x-ray optical components. A new fabrication process of Ta-on-SiN x-ray mask1 for x-ray optical components has been established. Tantalum is used for the x-ray absorber, because of having approximately the same absorption coefficient as that of gold. A thin SiN film, which has a high transparency for soft x rays, acts as a membrane supporting the Ta-absorbing patterns. The fabricated zone plates have an outermost zone width of 0.25 μm with up to 2 mm diameter. The pitch width of the transmission grating is 0.4 μm with up to 1.0 mm2 area. Adopting a highly brilliant and highly coherent undulator2 synchrotron radiation, we have been developing its optical system to apply to x-ray microscopy and holography. An x-ray microscope system3 consists of two kinds of zone plates with different dimensions for imaging and focusing undulator radiation. The resolving power of this microscope system was evaluated by using resolution test charts, which have the same structure as x-ray optical components. A resolution limit of 0.3 μm was obtained, which is very close to Rayleigh’s limit of 0.25 μm for the outer-most zone width. We constructed a divided wave-front interferometer with x-ray transmission gratings, and estimated the dispersion of undulator radiation to be 1/20. The authors thank S. Aoki of Tsukuba University for his useful discussion on x-ray optics. The authors are also grateful for the help from T. Tamamura and H. Yoshihara, NTT for fabrication of x-ray components, and from Y. Toyoshima of the Photon Factory in undulator experiments, respectively.