Patent ID: 7415694

Claim:
A computer-implemented method, for assigning phases to a plurality P 1 of light shifter polygons of a photolithographic mask, wherein the mask has a plurality of locations corresponding to a plurality P 2 of target features which are located between the shifter polygons, the method comprising: converting connectivity relationships between said plurality P 1 and said plurality P 2 into a graph by at least: representing each polygon in said plurality P 1 as a node in said graph; and representing a target feature in said plurality P 2 as a connection between two nodes, said two nodes representing two polygons with edges adjacent to said target feature; coloring nodes of said graph using said phases as colors by at least: assigning a first phase to a first node representing a first polygon in P 1 assigning a second phase to each node having a corresponding connection to the first node, said each node representing polygon in P 1 having an edge adjacent to a corresponding target feature in P 2 , said corresponding target feature representing said corresponding connection to the first node; and repeating said assignings with unassigned nodes in said graph thereby to result in phase assignments; and using said phase assignments to generate a representation of said photolithographic mask, wherein said target features represent opaque regions of the photolithographic mask bordered by said polygons representing openings in the photolithographic mask.