A mask pattern used in an optical exposure apparatus using a single wavelength comprises a light shielding film pattern which is produced on a transparent substrate, a pattern of transparent thin film for shifting the phase of exposure light which is produced at an aperture of the light shielding film pattern separated from the light shielding film pattern. Therefore, the resolution and the contrast of the pattern image projected on the wafer are enhanced, and the resolution and the depth of focus of photoresist which is to be patterned are improved. <IMAGE>