Flare and its impact on low-k 1 KrF and ArF lithography

Abstract

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 (PSF<SUB>scat</SUB>) 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 PSF<SUB>scat</SUB> 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.