1. A method of designing EB (electron beam) mask, comprising the steps of: (a) dividing an integrated circuit pattern into two complementary patterns; (b) scanning around one, as an object pattern, of small patterns included in one of said two complementary patterns, while measuring a distance from said object pattern to said small patterns adjacent to said object pattern; (c) registering a minimum of distances from said object pattern to said adjacent small patterns; and (d) changing a shape of at least one of said small patterns based on said minimum distance.