Deposition and characterization of B_4C/CeO_2 multilayers at 6.x nm extreme ultraviolet wavelengths

摘要

New multilayers of boron carbide/cerium dioxide (B_4C/CeO_2) combination on silicon (Si) substrate are manufactured to represent reflective-optics candidates for future lithography at 6.x nm wavelength. This is one of only a few attempts to make multilayers of this kind. Combination of several innovative experiments enables detailed study of optical properties, structural properties, and interface profiles of the multilayers in order to open up a room for further optimization of the manufacturing process. The interface profile is visualized by high-angle annular dark-field imaging which provides highly sensitive contrast to atomic number. Synchrotron based at-wavelength extreme ultraviolet (EUV) reflectance measurements near the boron (B) absorption edge allow derivation of optical parameters with high sensitivity to local atom interactions. X-ray reflectivity measurements at Cu-K_(alpha) (8 keV) determine the period of multilayers with high in-depth resolution. By combining these measurements and choosing robust nonlinear curve fitting algorithms, accuracy of the results has been significantly improved. It also enables a comprehensive characterization of multilayers. Interface diffusion is determined to be a major cause for the low reflectivity performance. Optical constants of B_4C and CeO_2 layers are derived in EUV wavelengths. Besides, optical properties and asymmetric thicknesses of inter-diffusion layers (inter-layers) in EUV wavelengths near the boron edge are determined. Finally, ideal reflectivity of the B_4C/CeO_2 combination is calculated by using optical constants derived from the proposed measurements in order to evaluate the potentiality of the design.