Metrology Target Layout for Tilted Patterns and Lower PPE

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Solution Overview

Problem

Current metrology targets in semiconductor manufacturing suffer from significant pattern placement errors due to optical aberrations, leading to discrepancies between metrology measurements and actual device features, especially for tilted patterns, resulting in inaccurate process control and measurement inaccuracies.

Innovation Solution

The method involves calculating Zernike sensitivity of pattern placement errors for both device and metrology target designs, using a cost function to select a target design that matches the device's sensitivity, and optimizing target design parameters to improve correspondence with device features, thereby reducing pattern placement errors and enhancing measurement accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional metrology targets are used for tilted device features, then measurement can be performed, but pattern placement errors increase due to optical aberrations

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidpattern placement error

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The patent modifies target design parameters including orientation angle, pitch, and dimensional characteristics to match the tilted device features. By changing these parameters, the target's diffraction pattern better corresponds to the device features under tilted illumination conditions, reducing pattern placement errors while maintaining measurement accuracy

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces asymmetric target designs with specific orientation angles that differ from conventional symmetric targets. This asymmetry allows the target to better represent tilted device features and their corresponding diffraction patterns, thereby reducing measurement discrepancies caused by optical aberrations

Inventive Principle:

Principle #4Asymmetry

2Ease of manufacture

If standard metrology target designs are used, then manufacturing simplicity is maintained, but correspondence to actual device features deteriorates

Engineering Contradiction:

Improvetarget manufacturing simplicityVSAvoiddevice feature correspondence

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent applies local quality by designing targets with specific regional characteristics - certain areas of the target have different orientations, pitches, or feature densities to locally match the corresponding device regions. This allows the target to accurately represent heterogeneous device features while maintaining overall manufacturing simplicity through standardized fabrication processes

Inventive Principle:

Principle #3Local quality

3Adaptability or versatility

If tilted device features are measured with conventional targets, then measurement coverage is achieved, but pattern placement error discrepancies increase by approximately 26%

Engineering Contradiction:

Improvemeasurement coverageVSAvoidpattern placement error discrepancy

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent segments the metrology target into multiple regions with different orientations and characteristics to cover various tilted device features. Each segment is optimized for specific measurement scenarios, allowing comprehensive measurement coverage while minimizing pattern placement errors for each individual feature type through localized optimization

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS12117347B2Metrology target design for tilted device designs

Publication Date: 2024.10.15 KLA CORP

AI summary

Metrology methods, modules and targets are provided, for measuring tilted device designs. The methods analyze and optimize target design with respect to the relation of the Zernike sensitivity of pattern placement errors (PPEs) between target candidates and device designs. Monte Carlo methods may be applied to enhance the robustness of the selected target candidates to variation in lens aberration and/or in device designs. Moreover, considerations are provided for modifying target parameters judiciously with respect to the Zernike sensitivities to improve metrology measurement quality and reduce inaccuracies.