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.
