Abstract:
The basic properties in the extreme ultraviolet (EUV) of one-dimensional
photonic crystals (Bragg reflectors) with incorporated superlattices are investigated by a numerical study using the multiple scattering method. The superlattice is realized in the “standard” Mo/Si system by periodically replacing certain Mo layers by Si layers. At 13.5 nm–the wavelength of interest for EUV lithography the superlattice sharpens the reflection peak
at normal incidence with only weak reduction of the peak value. Between normal incidence and total reflection at large angles, additional reflection peaks appear at certain angles where the reflection is zero for the
“standard” Mo/Si system. By combining different superlattices and depth
grading, the range of additional reflection peaks is extended towards
all-angle reflection. The effect of interface imperfections is considered for the
case of the interdiffusion of Mo and Si. The extension to other frequency
ranges is addressed via band structure calculations.