Theoretical investigation of pattern printability of oxidized Si and Ru capping models for extreme ultraviolet lithography (EUVL)

The optical performance of potential capping materials, Ru and Si, were quantitatively investigated by simulating the reflectivity on a mask and aerial image intensity transferred through the system. The reflectivity on the capping surface was calculated according to the capping thickness variation by using the Fresnel equation. For the calculation of the aerial image intensity, SOLID-EUV, which is capable of rigorous electromagnetic-field computation, was employed. Through the investigation of pattern image characteristics for partially oxidized capping models, the Ru capping model turned out to show a higher EUV reflectivity, smaller line variation, and a higher oxidation sensitivity compared to the case of the Si capping model. It could be reasonably concluded that Ru can be proposed as a potential capping material for achieving a better optical performance considering the experimentally proven high oxidation stability of the Ru capping model.