up operation to eliminate small dimension spaces followed by a size down operation on the remaining edges to produce a calculated layout the small dimension spaces are then identified by performing an u201c and not u201d operation between the calculated layout and the original layout the next step in the procedure for automatic generation of phase shift mask layouts involves identifying all corners in the structure inside corners and outside corners are identified outside corners are blocked to define ends of phase shift regions inside corners may result in a phase mismatches discussed above inside corners are blocked and thus provided with an extension of the opaque region such as a square extension and a shortening of the phase shift regions so that they do not extend all the way to the inside corner this square extension is applied in all inside corners whether a phase mismatch is found or not alternatively the extension is applied only where phase mismatches occur phase shift regions are formed in a simple case by copying the input structures in the minimum dimension features and shifting up and to the left for 180 degree or zero degree shifters and down and to the right for zero degree or 180 degree shifters the blocking regions formed for the outside corners cut the shifted regions at the ends of the input structures.