Influence of barrier interlayers on the performance of Mo/Be multilayer mirrors for next-generation EUV lithography

A comparative study was carried out of the structure and reflection performance of four types of multilayer mirror for extreme ultraviolet lithography at 11.2 nm; these were a pure Mo/Be structure and three Mo/Be-based structures with thin B₄C, C and Si interlayers. It was demonstrated that Mo/Be mirrors show maximum reflectance at normal incidence, while maximum structural perfection is shown by Mo/Be/Si mirrors. The introduction of B₄C and C layers into the structure increases the interlayer roughness and reduces the sharpness of the interfaces, adversely affecting the target coating characteristics. Results are presented for studies using four techniques: X-ray reflectometry, small-angle X-ray scattering, atomic force microscopy, and transmission electron microscopy.