Al/Mo/SiC Multilayer Diffraction Gratings with Broadband Efficiency in the Extreme Ultraviolet

Al/Mo/SiC periodic and aperiodic multilayers were optimized and deposited on high groove density gratings to achieve broadband efficiency in the extreme ultraviolet (EUV). Grating efficiencies were measured by monochromatic synchrotron radiation under 5° and 45° incident angles in the wavelength ranges 17-25 nm and 22-31 nm, respectively. We study the influence of the number of deposited periods on the initial trapezoidal profile and the EUV diffraction efficiency. We propose models of periodic and aperiodic coatings based on a combination of characterizations and compare rigorous coupled-wave analysis (RCWA) simulations with experimental data. We demonstrate the possibility to select the optimal balance between peak efficiency and bandwidth by adjusting the number of periods in the case of periodic multilayer grating. We also report unprecedented broadband diffraction efficiency with an Al/Mo/SiC aperiodic multilayer grating.