Overlay metrology system with direction-isolated imaging

Abstract

An overlay metrology system may include an illumination sub-system with one or more lenses that can direct illumination to an overlay target on a sample when implementing a metrology recipe. The illumination may include a first illumination dipole and a second illumination dipole. The overlay target may include two or more cells, where each cell may include first-direction features having periodicity along a first direction and second-direction features having periodicity along a second direction. The system may also include an imaging sub-system with an objective lens that can collect diffraction orders of the illumination generated by the overlay target and one or more detectors. The illumination sub-system and the imaging sub-system may be configured to generate a first image and a second image of the overlay target. A controller with one or more processors may generate overlay measurements based on the first and second images.

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