Segmented Metrology Targets for Asymmetric Aberration Estimation

Solution Overview

Problem

Existing semiconductor metrology technologies face challenges in accurately estimating and correcting for asymmetric aberrations, which affect the printing accuracy and measurement precision of semiconductor devices.

Innovation Solution

The development of metrology targets with segmented periodic structures having a 1:1 line-to-space ratio and fine pitches, where one structure lacks fine elements or has gaps, enhancing sensitivity to scanner aberrations, allowing for the estimation and correction of aberration effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional metrology targets are used, then manufacturing cost is reduced, but measurement precision deteriorates due to inability to accurately estimate asymmetric aberrations

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidtarget structure complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The metrology target is divided into multiple segmented periodic structures with different segment configurations. Each segment responds differently to asymmetric aberrations, enabling the system to estimate aberration effects by comparing the differential responses of the segmented structures.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces asymmetric features into the metrology target design, including structures with different line-to-space ratios (e.g., 1:1, 2:1, 3:1) and segment configurations. These asymmetric structures are specifically designed to be sensitive to asymmetric aberrations, allowing the system to detect and estimate aberration effects that would be invisible to symmetric targets.

Inventive Principle:

Principle #4Asymmetry

2Measurement precision

If complex aberration correction methods are used, then measurement precision improves, but device complexity and manufacturing cost increase

Engineering Contradiction:

Improveaberration estimation accuracyVSAvoidmanufacturing simplicity

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The metrology target is designed to self-diagnose asymmetric aberrations through its own segmented periodic structures. The target structures themselves serve as the sensing mechanism, eliminating the need for external calibration standards or complex correction equipment. The differential response of the segmented structures directly provides the information needed to estimate and correct for asymmetric aberrations.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent varies key geometric parameters of the periodic structures, including line-to-space ratios (1:1, 2:1, 3:1), segment configurations, and pitch dimensions. These parameter variations create structures with different sensitivities to asymmetric aberrations, enabling the system to estimate aberration effects through comparative measurement without requiring complex correction algorithms.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If simple metrology targets are used, then ease of manufacture is improved, but measurement precision deteriorates due to low sensitivity to scanner aberrations

Engineering Contradiction:

Improvetarget fabrication simplicityVSAvoidaberration sensitivity

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent introduces asymmetric features into the metrology target design, including structures with different line-to-space ratios (e.g., 1:1, 2:1, 3:1) and segment configurations. These asymmetric structures are specifically designed to be sensitive to asymmetric aberrations, allowing the system to detect and estimate aberration effects that would be invisible to symmetric targets.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent varies key geometric parameters of the periodic structures, including line-to-space ratios (1:1, 2:1, 3:1), segment configurations, and pitch dimensions. These parameter variations create structures with different sensitivities to asymmetric aberrations, enabling the system to estimate aberration effects through comparative measurement without requiring complex correction algorithms.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentEP3853665B1Estimation of asymmetric aberrations

Publication Date: 2023.12.20 KLA CORP

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Figure 3~4B
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AI summary

Metrology targets, target design methods and metrology measurement methods are provided, which estimate the effects of asymmetric aberrations, independently or in conjunction with metrology overlay estimations. Targets comprise one or more pairs of segmented periodic structures having a same coarse pitch, a same 1:1 line to space ratio and segmented into fine elements at a same fine pitch, wherein the segmented periodic structures differ from each other in that one thereof lacks at least one of its corresponding fine elements and/or in that one thereof comprises two groups of the fine elements which are separated from each other by a multiple of the fine pitch. The missing element(s) and/or central gap enable deriving the estimation of aberration effects from measurements of the corresponding segmented periodic structures. The fine pitches may be selected to correspond to the device fine pitches in the corresponding layer.