1. A photomask comprising: a substrate that is transparent to a source of illumination; and a masking material layer over the substrate, the masking material layer comprising a plurality of patterned mask features, the plurality of patterned mask features comprising: a two-dimensional array of parallel mask features, wherein pairs of the parallel mask features share an end-to-end region between the parallel mask features of each pair and wherein an imaginary axis bisects the end-to-end regions; and a one-dimensional array of assist features, each assist feature being located proximate to at least one end-to-end region and wherein the imaginary axis intersects each assist feature.