A major challenge of low-k1 microlithography that has to be addressed by any photomask defect
detection strategy is the complex relation between the signal of the defect in the detector and its
impact, in terms of printing errors, on the processed wafer. This non-trivial relation is immanent to
the large MEEF values characterizing lithography at sub-wavelength features. One common method
to work around this problem is to use aerial imaging optics which emulates the stepper exposure
process. Currently available aerial inspection and review tools based on the well established fact that
CD variation in the aerial image closely represents the CD variation on the wafer. Published
literature explains why a defect's printing effect can be captured, with high correlation, by aerial
Here we describe a novel connection between a defect's detection signal and the printed CD
variation on an adjacent pattern. This connection can be exploited by aerial imaging mask inspection
systems to ensure that their detection thresholds are set to detect CD variation of a given threshold.
We show that under aerial imaging conditions, the defect signal and CD variation are linearly related,
regardless of defect's attributes, provided that the defect resides close to a pattern's transition edge,
or is surrounded by a dense pattern.
We present experimental results, demonstrating this linear scaling between the defect signal and CD
variation, and show practical application results of aerial imaging mask inspection, with implications
to production mask fab.