Patent ID: 7550235

Claim:
A method of generating a mask design having optical proximity correction features disposed therein, said method comprising the steps of: obtaining a target pattern having features to be imaged on a substrate; generating a first interference map based on said target pattern, said first interference map defining areas of constructive interference between at least one of said features to be imaged and a field area adjacent said at least one feature; placing a first set of assist features having a first phase in the mask design based on the areas of constructive interference defined by said first interference map; generating a second interference map based on said first set of assist features, said second interference map defining areas of constructive interference between assist features of said first set of assist features and a field area adjacent at least one of said assist features of said first set of assist features; and placing a second set of assist features having a second phase in the mask design based on the areas of constructive interference defined by the second interference map, wherein said first phase does not equal said second phase.