Simulating photomask edge roughness and corner rounding

Corner rounding and edge roughness of a rectangular opening at a glass-chrome mask are simulated with TEMPEST. The intensity patterns on the image plane are extracted and compared for these defects at several degrees of fabrication-induced imperfection. A 4X - DUV (lambda=248nm) lithography printing system is assumed with NA=0.6 and sigma=0.5. The prototypical geometry simulated was a 4um x 1um line on the mask (1um x 0.25um on the wafer). The results indicate that the rounding of the corners does not decrease the printed area by more than 2% for a 0.4um radius corner rounding and that roughness should not be a concern, at least in DUV, since it does not crucially affect the linewidth of the printed area.