Mirror-Image Overlay Marks for Bottom Grating Asymmetry Compensation

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Solution Overview

Problem

Conventional overlay marks in semiconductor manufacturing suffer from reduced accuracy due to asymmetry in the bottom layer gratings, leading to inaccuracies in overlay alignment between different layers.

Innovation Solution

The proposed solution involves designing overlay marks with upper and lower layers that include mirror-image gratings to cancel out asymmetry errors, utilizing a specific pattern and spacing to ensure accurate alignment by compensating for asymmetries in the bottom layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional overlay marks with asymmetric bottom layer gratings are used, then the overlay mark structure is simple, but the measurement accuracy of overlay alignment is reduced due to asymmetry-induced diffraction errors

Engineering Contradiction:

Improveoverlay measurement accuracyVSAvoidoverlay mark structure complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent applies asymmetry principle by intentionally designing the bottom layer gratings with asymmetric profiles (different left and right sidewall angles) and introducing asymmetric dummy gratings. The asymmetric dummy gratings are positioned to compensate for the asymmetry-induced diffraction errors from the actual gratings, thereby improving overlay measurement accuracy while maintaining a relatively simple overall structure.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent implements preliminary anti-action by pre-calculating the asymmetry errors that will be introduced by the bottom layer grating asymmetry and designing dummy gratings that produce opposite and equal diffraction effects. This preliminary compensation design eliminates the need for complex real-time correction during measurement, directly improving overlay measurement accuracy.

Inventive Principle:

Principle #9Preliminary anti-action

2Ease of manufacture

If asymmetric bottom layer gratings are used in overlay marks, then manufacturing is easier, but additional diffraction orders are induced that reduce overlay accuracy

Engineering Contradiction:

Improveoverlay mark fabrication easeVSAvoidoverlay alignment accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent converts the harmful effect of asymmetry-induced diffraction into a beneficial compensation mechanism. By intentionally introducing asymmetric dummy gratings that produce diffraction orders opposite to those from the asymmetric bottom layer gratings, the harmful diffraction effects are transformed into useful compensation signals that improve overlay measurement accuracy.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Measurement precision

If mirror-image gratings are used to cancel asymmetry errors, then overlay accuracy is improved, but the overlay mark design and fabrication complexity increases

Engineering Contradiction:

Improveoverlay measurement accuracyVSAvoidoverlay mark pattern complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent applies segmentation by dividing the overlay mark into distinct functional regions: actual gratings for measurement, asymmetric dummy gratings for compensation, and mirror-image gratings for error cancellation. This segmentation allows each component to perform its specific function independently, improving overall measurement accuracy while maintaining manageable fabrication complexity through modular design.

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach enhances overlay accuracy by canceling out asymmetry-induced errors, resulting in improved alignment between layers during semiconductor fabrication.

Implementation Method 1

The asymmetry in the bottom gratings can induce additional diffraction orders, resulting in reduced overlay accuracy.

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS12554206B2Overlay marks for reducing effect of bottom layer asymmetry

Publication Date: 2026.02.17 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

Methods of fabricating and using an overlay mark are provided. In some embodiments, the overlay mark includes an upper layer and a lower layer disposed below the upper layer. The lower layer includes a first plurality of compound gratings extending in a first direction and disposed in a first region of the overlay mark, each of the first plurality of compound gratings including one first element and at least two second elements disposed on one side of the first element, and a second plurality of compound gratings extending the first direction and disposed in a second region of the overlay mark, each of the second plurality of compound gratings including one third element and at least two fourth elements on one side of the third element. The first plurality of compound gratings is a mirror image of the second plurality of compound gratings.