Sub-resolution assist features (SRAF) insertion using a mask synthesis process based on pixel-based mask optimization schemes has been studied in recent years for various lithography schemes, including 6% attenuated PSM (attPSM) with off-axis illumination such as Quasar. This paper will present results of the application of the pixel-based optimization technology for 6% and 30% attPSM cases, using random contact hole patterns to compare and examine imaging properties of MEEF, CD uniformity, and side-lobe printing. We will also discuss practical approaches for manipulation of complex shapes generated by the pixel-based optimization to address mask manufacturability issues.

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