Peak and integrated reflectivity, wavelength and gamma optimization of Mo/Si, and Mo/Be multilayer, multielement optics for extreme ultraviolet lithography

Reported is the optimization of the fabrication of Mo/Si multilayer systems produced by e-beam evaporation and ion-beam smoothening. The impact of a number of coating parameters is verified such as variation of the mirror’s center wavelength and the metal fraction of the bilayer (Γ ratio), resulting in reflectivities up to 68.6% at normal incidence. Parallel to this experimental work, a numerical optimization based on experimentally determined multilayer properties is carried out on the throughput of multimirror lithographic systems for the 11–15 nm wavelength region using Mo/Si and Mo/Be coatings. The center wavelength, Γ ratio and layer stack have been optimized. The calculations show an optimum throughput for a 10-mirror Mo/Si system at 14.4 nm, assuming a light source with a wavelength independent spectrum.