Patent ID: 8628897

Claim:
An extreme ultraviolet lithography (EUVL) process, comprising: receiving an extreme ultraviolet (EUV) mask, including: a first main polygon; a second main polygon adjacent to the first main polygon; a plurality of assist polygons; and a field (a region without main polygons and assist polygons), wherein each of the main polygons, the assist polygons, and the field has an associated state, wherein the state assigned to the first main polygon is different from the state assigned to the second main polygon, and wherein the plurality of assist polygons are assigned the same state, which is different from the state assigned to the field; exposing the EUV mask by a nearly on-axis illumination (ONI) with partial coherence σ less than 0.3 to produce diffracted lights and non-diffracted lights; removing a portion of the non-diffracted lights; and collecting and directing the diffracted lights and the not removed non-diffracted lights by a projection optics box (POB) to expose a target.