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Abstract

A method for diagnosing a lithographic tool. The method includes developing digitalized images of at least one wafer pattern with different exposure doses and assembling the digitized images into a pupilgram. The at least one function is of a known illuminator behavior of the lithographic tool is modeled. The pupilgram is fitted to the modeled function to determine whether a behavior associated with the pupilgram is within predetermined limits of illuminator behavior to diagnosis imperfections in the illuminator behavior. One technique applied to the illuminator analysis consists of evaluating the dose transmitted (by direct calculation) by the lens for a given input pupilgram (or set of pupilgram basis functions), a given pattern size and pitch, and a defined lens NA, is described. This transmitted dose is calculated and displayed as a function of position within the illumination distribution (pupilgram), and is valuable for the highlighting of those parts of the illumination distribution that contribute the largest amount of relative dose to the imaging process, and to compare the dose transmitted by different orientations of the same pattern.

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