Patent ID: 6911286

Claim:
A method of designing a phase grating pattern, the method comprising: selecting a target pattern to be formed on a wafer via a photolithographic process; selecting a mask pattern of a primary mask, and which mask pattern is to be transcribed onto the wafer in the photolithographic process; dividing an area, corresponding to at least one portion of the area of the primary mask, into a plurality of subcells; arbitrarily assigning one of a plurality of phase values to the subcells, whereby each of the subcells is provided with an initial one of the phase values, each of the phase values representing a respective phase shift that exposure light of the photolithographic process will undergo by being transmitted through a region of the phase grating pattern corresponding to the subcell; randomly selecting one of the subcells, and assigning one of the plurality of the phase values to the selected one of the subcells, and repeating said random selecting of respective ones of the subcells and said assigning of one of the phase values thereto such that a plurality of arrangements of phase values assigned to the subcells are produced; and evaluating the plurality of arrangements of phase values with respect to the propensity of a phase grating pattern, based on an arrangement of the phase values, to produce a form of modified illumination for the primary mask that is optimal for producing the target pattern being on the wafer when an exposure light is directed onto the mask via the phase grating pattern in the photolithographic process.