Method and device for writing photomasks with reduced mura errors

Abstract

The problem of mura in large area photomasks is solved or at least reduced by setting up a writing system to write a pattern with high accuracy and with the optical axes essentially parallel to the movement axes of the stage, then writing photomasks in two passes with the substrate rotated to different angles on the stage. The angle between the orientation of the first and second pass is larger than about 10 degrees, larger than about 20 degrees or larger than about 35 degrees and it can be approximately 10 degrees, approximately 50 degrees, approximately 60 degrees or approximately 90 degrees. The substrate is physically rotated on the stage and aligned with high accuracy after the rotation and the data driving the first and second exposure passes are derived from the first input data specification but processed according to the known oblique angles, so that the second pass is accurately overlaid on the first pass.

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