Patent ID: 8495529

Claim:
A method, implemented by a computer, of improving imaging performance of a mask pattern having a feature to be imaged, said method comprising the steps of: (a) obtaining a model of a lithographic process for imaging said mask pattern onto a substrate; (b) determining an optimal setting of said lithographic process to be utilized when imaging said mask pattern; (c) determining, using said model, a first interference map based on said mask pattern and said optimal setting; (d) determining a first seeding site representing the optimal placement of an assist feature within said mask pattern relative to said feature to be imaged on the basis of said first interference map; (e) selecting a plurality of lithographic process settings that represent a predefined amount of variation relative to said optimal setting; (f) determining, using said model, a plurality of interference maps respectively based on said mask pattern and said plurality of lithographic process settings; (g) determining a plurality of seeding sites representing the optimal placement of an assist feature within said mask pattern relative to said feature to be imaged on the basis of said plurality of interference maps; and (h) generating an assist feature having a shape which encompasses both said first seeding site and said plurality of seeding sites, wherein one or more of steps (a)-(f) are performed using said computer.