Sub-resolution assist feature to improve symmetry for contact hole lithography

摘要

A method of making a mask design having optical proximity correction features is provided. The method can include obtaining a target pattern comprising a plurality of target pattern features corresponding to a plurality of features to be imaged on a substrate. The method can also comprise generating a mask design comprising mask features corresponding to the plurality of features to be imaged on the substrate and controlling the aspect ratio of at least one of the features of the plurality of features to be imaged on the substrate by positioning a sub-resolution assist feature proximate to the corresponding mask feature.