A system and process of an extreme ultraviolet lithography (EUVL) is disclosed. The system and process includes receiving a mask with two states, which have 180 degree phase difference to each other. These different states are assigned to adjacent main polygons and adjacent assist polygons of the mask. A nearly on-axis illumination (ONI) with partial coherence σ less than 0.3 is utilized to expose the mask to produce diffracted lights and non-diffracted lights. A majority portion of the non-diffracted lights and diffracted light with diffraction order higher than 1 are removed. Diffracted light having +1-st and −1-st diffracted order are collected and directed by a projection optics box (POB) to expose a target.