Ellipsometric imaging for optical defect inspection

Abstract

Methods and systems for generating bright-field ellipsometric images indicative of structural defects sized below the optical resolution limit are presented herein. In some examples, bright-field ellipsometric images offer a higher signal to noise ratio of small defect signals to nuisance pattern noise signals compared to dark-field imaging at the null condition. Various ellipsometric imaging techniques are employed to generate images of a wafer or reticle under inspection. The images provide intensity contrast that is indicative of phase differences induced by the scattering response of different structures in the imaging field of the ellipsometric imaging system. In one aspect, an ellipsometric imaging system employs a polarizer in the illumination path and an analyzer and at least one waveplate in the imaging path. The ellipsometric imaging system generates images having intensity differences that differentiate defects of interest from nuisance pattern noise with relatively high signal to noise ratio.

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