A method for transferring a pattern from a mask to a substrate (or wafer), comprises dividing a mask generation data file into a plurality of segments. The segments include a main pattern area and a stitching area. Each stitching area contains a respective common pattern. An image of an illuminated portion of the main pattern area is formed. Connection ends of the segments in a substrate area (or wafer area) are illuminated with an illumination beam. An image of the illuminated portion of the main pattern area is formed, and a halftone gray level dosage distribution is produced in the substrate area (or wafer area) corresponding to the common pattern. The common patterns of adjacent segments substantially overlap in the substrate area (or wafer area).