Extending depth of field for dark-field wafer surface inspection systems using digital holography

Zhenzhen Ding; Min Xu; Xinlan Tang; Fei Yu

doi:10.1117/12.3046482

13 November 2024 Extending depth of field for dark-field wafer surface inspection systems using digital holography

Zhenzhen Ding, Min Xu, Xinlan Tang, Fei Yu

Author Affiliations +

Proceedings Volume 13280, Advanced Optical Manufacturing Technologies and Applications 2024; and Fourth International Forum of Young Scientists on Advanced Optical Manufacturing (AOMTA and YSAOM 2024); 132800G (2024) https://doi.org/10.1117/12.3046482
Event: Second Conference on Advanced Optical Manufacturing Technologies and Applications & Fourth Forum of Young Scientists on Advanced Optical Manufacturing, 2024, Xi'an, China

Abstract

Dark-field imaging systems demonstrate significant advantages in the field of unpatterned wafer front-end defect inspection attributed to their high sensitivity, low cost, and high throughput. However, as optical systems with large numerical apertures (NA) are applied and inspection wavelengths gradually extend into the ultraviolet range, optical systems become extremely sensitive to defocusing. Surface variations on the wafer in the order of micrometers can cause complete defocusing in optical systems, leading to false positives and false negatives. To address this issue, this paper introduces a depth of field (DOF) extension method for dark-field inspection systems based on digital holography. Digital refocusing techniques is used to calculate the image stack at different focal depths based on the scattered light wave-front reconstructed from the hologram, and a focus measurement function evaluates each image to determine the optimal focal position. Finally, images near the optimal focal point are fused to create an all-in-focus image containing defect information on the wafer surface. The comparison between the processed results with the well-focused portions of the real captured images shows that the method accurately restores the distribution of defects on the wafer surface. The post-processing method extends the DOF of the optical system without compromising scanning efficiency, providing a solution to the defocusing issue in dark-field inspection systems for wafers.

(2024) Published by SPIE. Downloading of the abstract is permitted for personal use only.

Citation Download Citation

Zhenzhen Ding, Min Xu, Xinlan Tang, and Fei Yu "Extending depth of field for dark-field wafer surface inspection systems using digital holography", Proc. SPIE 13280, Advanced Optical Manufacturing Technologies and Applications 2024; and Fourth International Forum of Young Scientists on Advanced Optical Manufacturing (AOMTA and YSAOM 2024), 132800G (13 November 2024); https://doi.org/10.1117/12.3046482

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KEYWORDS

Semiconducting wafers

Inspection

Digital holography

Imaging systems

Image fusion

Depth of field

Digital imaging

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