System and method for lateral shearing interferometry in an inspection tool

IL305113BActive Publication Date: 2026-08-01KLA CORP
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Patent Information

Application Number
IL305113
Authority / Receiving Office
IL · IL
Patent Type
Patents
Current Assignee / Owner
Priority Date
2022-04-18
Filing Date
2022-04-21
Publication Date
2026-08-01
Estimated Expiration
2042-04-21

AI Technical Summary

Technical Problem

Current defect inspection tools for photolithographic masks and wafers face challenges in accurately capturing wave front aberrations due to thermally induced drift and mechanical alignment changes, with existing methods suffering from limited dynamic range, high measurement times, and inability to discriminate between amplitude and phase errors.

Method used

The implementation of an in-situ wave front metrology system based on lateral shearing interferometry (LSI) that uses a reflective mask grating structure and optical elements to provide phase reconstruction and identify changes in the wave front of light, enabling high-end accuracy and faster measurement times by discriminating between intensity and phase errors.

Benefits of technology

This solution provides a single metrology method with a large capture range, higher accuracy, and shorter integration times, capable of measuring all Zernike coefficients, thereby mitigating the risk of 'blind spots' and effectively tracking performance drift in optical setups.

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Abstract

A method for in-situ wave front detection within an inspection system is disclosed. The method includes generating light with a light source and directing the light to a stage-level reflective mask grating structure disposed on a mask stage. The method includes directing light reflected from the stage-level reflective structure to a detector-level mask structure disposed in a plane of a detector and then collecting, with an optical element, light reflected from the detector-level mask structure. The method includes forming a pupil image on the detector and laterally shifting the stage-level reflective mask, with the mask stage, across a grating period of the stage-level reflective mask grating structure to provide phase reconstruction for lateral shearing interferometry. The method includes selectively impinging light reflected from the optical element on the one or more sensors of the detector.
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