The evolution of high-NA projection optics design and manufacturing tolerances has been remarkable in
recent years. Nevertheless, different instances of identical scanner models can still exhibit unique optical
fingerprints which can impart subtle patterning differences for a given mask exposed at nominally identical
conditions on different scanners. In some cases, a product can be shown statistically to yield lower when a
certain layer is exposed on a particular scanner. Thus it is common to have a certain subset of the total
population of tools allowed for certain critical levels, such as gate. Since a single mask is typically shared
between the multiple allowed scanners, the optical proximity correction model which is employed in the
generation of that mask must represent the average fingerprint of those tools.

This paper investigates the use of tool-specific optical models to elucidate the intersection of design and process variability, which will manifest differently on each scanner, depending upon subtle details of the scanner fingerprint.

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