Optimal phase shift and reflectance for high numerical aperture EUV phase shift mask

As semiconductor technology became more integrated, the numerical aperture (NA) of extreme ultraviolet (EUV) exposure technology has increased from 0.33 to 0.55 to realize finer patterning. High NA EUVL aims to enable 8 nm half pitch resolution. As the NA increases and a smaller linewidth needs to be implemented, the mask 3D effects on patterning will become more severe. For mass production of EUV, it is essential to find an optimal absorber structure to alleviate serious problems such as mask 3D effects and shadowing effects. Among the various factors constituting the EUV photomask, phase shift and reflectance of the absorber are the most important factors that determine the image quality. Through computational simulation, the optimal structure was selected in consideration of phase shift and reflectance, and imaging performance and process latitude were calculated.