Angular dependency of off-axis illumination on 100-nm-width pattern printability for extreme ultraviolet lithography: Ru/Mo/Si reflector system

The pattern printability of the Ru/Mo/Si system was quantitatively investigated by two successive schemes, reflectivity of the mask, and aerial image intensity transferred through the system. The reflectivity of a Ru/Mo/Si reflector was calculated and compared with the value of Mo/Si reflector for various incident angles (0°–5°) using Fresnel equation. In order to verify angular dependency of aerial image intensity in a Ru/Mo/Si reflector, we employed SOLID-EUV, which is capable of rigorous electromagnetic field computation. In the calculation, 100 nm line and space pattern was generated by 2D mask geometry with perfect absorber of opaque material. Through the investigation of the angular dependency on the pattern printability of Ru/Mo/Si and Mo/Si reflectors, we could suggest the optimal reflector system for specific condition of incident angle, i.e., Ru/Mo/Si system for ≲ 3 ° and Mo/Si system for ≳ 4 ° for maximizing optical performance of the EUVL system.