Flare and its impact on low-k1 KrF and ArF lithography

We present a complete method for the characterization and modeling of flare based on the measurement of the modulation transfer function (MTF) of scanners. A point-spread function (PSFscat) representing only the scattered light or flare in the tool is inferred by comparing the measured MTF with a calculated MTF for aberration-free imaging. This PSFscat is then used to predict the effect of flare for different layouts. In particular, local variations in pattern density are shown to couple with mid- and short-range flare and lead to significant CD non-uniformity across the field. Finally, we examine double exposure techniques that are sensitive to flare because of the total light reaching the wafer, from the two masking steps.

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