US Patent 7141338 Sub-resolution sized assist features

Corner rounding and image shortening is substantially reduced in an image printed on a substrate by illuminating a photolithographic mask and projecting light transmitted through the photolithographic mask onto the substrate using an optical projection system. The photolithographic mask has a mask pattern that includes at least one printable feature having at least one corner. Incorporated, in the mask pattern, is at least one line feature corresponding to the corner of the printable feature. The line feature is in at least close proximity to the corresponding corner of the printable feature and has a line width that is smaller than a minimum resolution of the optical projection system.