Disturbance Effects in Extreme Ultraviolet Interferometric Lithography Affecting Interference Fringes

We set up an extreme ultraviolet (EUV) interferometer lithography tool dedicated to the study of the photoresist properties at the EUV wavelength. Two coherent beams are recombined to generate a standing wave, which can be recorded in a photoresist. However, other physical phenomena are generated by the interferometer structure which can disturb the quality of interference fringes. The Fresnel effect is one of these phenomena which is fully detailed in this work. Accurate numerical models have been compared to experimental studies to quantify the reduction of the interference area by the Fresnel effect. Depending on the Fresnel number (NF), several advantageous conditions are presented in order to reduce the Fresnel disturbance on resist.