The imaging quality of extreme ultraviolet lithography (EUVL) depends on the optical properties, the thickness of the mask absorber material, and the illumination shape of the source. For high numerical aperture (NA) mask absorbers, we can analyze how to mitigate their mask three-dimensional (M3D) effects based on waveguide effects using test light sources. Then, we can improve key metrics such as the normalized image log slope (NILS), the (BFV), the throughput criterion (TpT), the threshold to size (TtS), and the critical dimension (CD) error of the aerial images. This study effectively screens high-NA EUV mask absorber materials based on the waveguide effect in the absorber. It provides a reasonable explanation for the imaging trend, presents a method to improve the screening efficiency of absorber materials, and determines the final absorber material parameters suitable for high-NA lithography systems by considering the limitations of actual materials and the results of lithography simulation. The above research has potential to experience for the selection of absorber materials in future hyper NA lithography systems.
Liu et al. (Wed,) studied this question.