Method of correcting mask pattern

A method of correcting a mask pattern to obtain a desired mask pattern that corresponds to a design pattern by optical lithography, comprising the steps of:

• defining a pattern edge of said mask pattern based on a two-dimensional light intensity distribution in a whole area of the mask pattern;
• setting positions in said design pattern, which have a smallest deviation and have a largest deviation between the pattern edge of the mask pattern and a pattern edge of said design pattern, as a close point and an isolated point, respectively;
• selecting an edge to be corrected by making a slight amount of correction to the pattern edge of the mask pattern located within a specified distance from said isolated point, calculating variations of light intensities at positions, which correspond to said close point and said isolated point, and then selecting the edge to be corrected which has a smaller variation of the light intensity at the close point and a larger variation of the light intensity at the isolated point by the correction;
• correcting the edge to be corrected, calculating the light intensity at the close point and the light intensity at the isolated point after the correction, selecting the edge to be corrected one more time when the light intensity at the close point is not within a specified criterion for edge selection, correcting said edge to be corrected one more time when the light intensity at the isolated point after the correction does not satisfy a specified criterion, and repeating the selection of said edge to be corrected and the correction of said edge to be corrected until the light intensities at the close point and the isolated point both satisfy the criterions;
• defining a pattern edge to be corrected based on the secondary light intensity distribution of the whole area of the mask pattern, of which said edge to be corrected is corrected;
• and
• determining completion of correcting said mask pattern when a deviation between the pattern edge to be corrected and the pattern edge of the design pattern is within a specified criterion for determining completion of the correction.