Improved goals for diffraction-based superposition error measurement

By shifting grid patterns on thin film layers to break symmetry and reduce optical crosstalk, the method addresses measurement inaccuracies in small targets, enhancing the accuracy of superposition error estimation and improving photolithography yield.

JP2026121425APending Publication Date: 2026-07-24KLA CORP
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Patent Information

Authority / Receiving Office
JP · JP
Patent Type
Applications
Current Assignee / Owner
KLA CORP
Filing Date
2026-05-12
Publication Date
2026-07-24

AI Technical Summary

Technical Problem

Existing superposition measurement tools face challenges in accurately measuring overlay errors in semiconductor circuits due to optical crosstalk in small scattering measurement targets, particularly those with dimensions reduced to 5 μm × 5 μm or less, leading to significant errors in measurement results.

Method used

The method involves designing an overlay target with grid patterns on two thin film layers, where each grid is shifted by predetermined displacements in both x and y directions relative to the other, breaking symmetry and reducing optical crosstalk by ensuring both ends of the rods contribute positively to the scattering measurement signal without introducing errors, using a mask set to pattern these grids.

Benefits of technology

This approach enhances the accuracy of superposition error measurement by mitigating optical crosstalk, enabling precise estimation of overlay errors even in small targets, thereby improving the yield in the photolithography process.

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Abstract

This invention provides an improved design for a superposition target used in scattering measurements, along with a measurement method using a superposition target. [Solution] The method includes the steps of depositing first and second overlapping thin film layers on a semiconductor substrate and patterning the layers to define an overlay target. The target includes a first grid pattern in the first layer, which includes a first linear grid oriented in a first direction and a second linear grid oriented in a second direction perpendicular to the first direction, and a second grid pattern in the second layer, which includes a third linear grid identical to the first linear grid and a fourth linear grid identical to the second linear grid. The second grid pattern is shifted from the first grid pattern by nominal offset amounts, which are first and second displacements in the first and second directions. A scattering measurement image of the substrate is acquired, and the overlay error between the patterns of the first and second layers is estimated.
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Citation Information

Patent Citations

  • US20190250521A1