Thermal stability of Co SiO2 multilayers for use in the soft x-ray region

The thermal stability of Co SiO2 multilayers was evaluated. Multilayer samples were deposited on Si substrates by means of the ion beam sputtering method and annealed at temperatures from 100 °C to 600 °C in a vacuum furnace. For the structural and optical evaluations, small-angle x-ray diffraction measurements, soft x-ray reflectivity measurement in the 1 keV energy region, and transmission electron microscopy observations were carried out. As the results, the Co SiO2 multilayers annealed up to 400 °C maintained the initial multilayer structure, and kept almost the same soft x-ray reflectivity as the as-deposited sample. A deterioration of the multilayer structure caused by the growth of cobalt grains was found on the samples annealed over 500 °C, and the soft x-ray reflectivity dropped in accordance with the deterioration of the multilayer structure.