In one embodiment, a spacing is determined for each edge of a number of
features in a photolithographic design. The edges have at least a
partially predictable layout. Based on the spacing and the predictable
layout, a bridge structure is generated. Each bridge of the bridge
structure connects one of the edges to an edge of a neighboring feature.
Then, the features and the bridge structure are provided for a phase
assignment. The phase assignment assigns features at opposite ends of
each bridge in the bridge structure to opposite phases. In another
embodiment, a sub-resolution assist feature (SRAF) is introduced for an
edge of a feature and a bridge is generated from the feature to the SRAF.
Then, the feature and the SRAF are assigned to opposite phases based on
the relationship defined by the bridge.