Simulation and analysis of multilayer film for EUV lithography

Extreme ultraviolet lithography uses a light source with a wavelength of about 10nm-14 nm for illumination, and almost all known optical materials have strong absorption in this band. Therefore, the extreme ultraviolet lithography optical systems used reflective design, the reflective optical elements need to be coated with multilayers film to improve reflectivity. The choice of multilayers material and thickness of reflective optics is a key factor affecting their reflectivity in this wavelength bands. Currently, Mo/Si multilayer thin-film reflectors are used in extreme ultraviolet lithography optical systems. And in the 10nm-20nm band, Nb/Si multilayer films can also be used. In this research, the influence of factors including incident angle, operating wavelength, and film thickness on the corresponding reflectance of two multilayer reflective film structures is analyzed through mathematical modeling using Mathcad.