Impact of mask defect in a high MEEF process
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In this paper, we demonstrated the impact of illumination condition on MEEF and investigated the correlation between CD linearity and MEEF according to the illumination conditions and imaging pitches. For all of the illumination conditions, the MEEF increased appreciably as the CD decreased beyond a CD linear region. The aerial image intensity and NILS change with the pattern size and illumination conditions were also investigated. We also measured and analyzed the printability of mask defect according to the MEEF. Two types of mask defects; chrome and clear mask intrusion defects were designed in the cell. The designed mask defect was split from 0.02 μm2 to 0.72 μm2(5X) in area. While within a linear CD region the slope of the CD response to the defects are similar regardless of the illumination condition and 0.08 μm2(5X) clear defect size was not printed, within a linear CD region the slope of the CD response to the defects increased as the illumination NA decreased and only 0.02 μm2(5X) chrome defect size was printed within a linear CD region, where the defect printability criteria is out side ±5% target CD range. We could also show that as the process is operated under the linearity limit, the dependency of aspect ratio to the defect printability would be increased.