Optical proximity correction method utilizing serifs having variable dimensions

A method of forming a mask for transferring a lithographic pattern onto a substrate by use of a lithographic exposure apparatus, said pattern comprising a plurality of features each of which has corresponding edges and vertices, said method comprising the steps of:

• forming a serif on a plurality of said vertices contained in said lithographic pattern, each of said serifs having a substantially rectangular shape, and
• determining the size of each serif independently on the basis of the length of the feature edges forming a given vertex, and a first distance and a second distance from the given vertex to the nearest feature edge, said first distance and said second distance corresponding to a first direction and a second direction, respectively, which are substantially perpendicular to one another and within the plane of the mask pattern,
• wherein the position of each side of a given serif is independently adjustable relative to the positions of the remaining sides of the given serif.