Lamellar Columns Photonic Crystal Mirror with High Reflectivity for Extreme-Ultraviolet Radiation

Abstract

For the applications in the extreme ultraviolet (EUV) region, early research [1] revealed that the suitable design of multilayer mirrors with a wavelength of 5 to 50 nm can increase the reflectivity. Li et al. have done related research on Mo/Si multilayer films and proposed vacuum voids mixing in the Si layer can be used to increase the reflectivity for EUV radiation [2]. It is found that the higher proportion of vacuum voids, the higher reflectivity can be obtained from 73.43% for no vacuum voids to 83.24% for full vacuum voids. According to [2], the reflectivity can be effectively improved by vacuum mixing Si layers in 40 pairs of Mo/Si multilayer films. Mo has a larger extinction coefficient than Si in the 13.5 nm wavelength region, so Mo is designed as an absorber to localize into the low-intensity standing wave field. By using a Si layer mixed into the vacuum, the high-intensity regions will have a smaller extinction coefficient, i.e. the imaginary part of the refractive index. The reflectance can be improved by mixing the Si layer in vacuum is because it has more difference between the real parts of the refractive index of the Si layer and the Mo layer; thereby, the interference effect is enhanced. For the multilayer columnar structure mixed into the vacuum layer [3], there are also related researches on the applications in the visible light region. It is not yet found to use similar kinds of structures in extreme ultraviolet light region. In this paper, we propose a hybrid Mo/Si multilayer cylinder-film in control of the constructive interference in multilayer films to enhance reflectivity of EUV radiation.