Oblique illumination for overlay metrology

The overlay metrology system uses oblique illumination with two diffraction orders to enhance imaging contrast and accuracy for small, high-density features, addressing measurement challenges in overlay metrology.

JP7828361B2Active Publication Date: 2026-03-11KLA CORP
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Patent Information

Authority / Receiving Office
JP · JP
Patent Type
Patents
Current Assignee / Owner
Filing Date
2022-04-18
Publication Date
2026-03-11

AI Technical Summary

Technical Problem

Overlay metrology systems face challenges in accurately measuring the alignment of small, high-density features due to increased demands on characterization as feature sizes decrease.

Method used

An overlay metrology system using oblique illumination with two diffraction orders, specifically the zeroth-order and a single first-order diffraction lobe, to enhance imaging contrast and reduce sensitivity to sample defocus, enabling measurement of finer pitches.

Benefits of technology

This approach provides high-contrast imaging robust to defocus errors and allows measurement of smaller pitch targets, improving measurement accuracy and relaxes measurement conditions.

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Abstract

The overlay metrology system may include an overlay metrology tool suitable for measuring an overlay target on a specimen, the overlay target including one or more grating structures with patterned features distributed along one or more measurement directions. The overlay metrology tool may include an objective lens and an illumination path for illuminating the overlay target with two or more oblique illumination lobes distributed in one or more illumination intensity distributions, such that for each of the measurement directions, diffraction orders of the one or more illumination intensity distributions by the overlay target collected by the objective lens exclusively include a zeroth order diffraction lobe and a single first order diffraction lobe from at least one of the two or more illumination lobes. The overlay metrology tool may further include at least one detector for imaging the specimen and a controller for generating overlay measurements based on the images.
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Citation Information

Patent Citations

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    JP2017537317A

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    JP2019507368A

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    JP2019526053A