Metrology Sensor Spatial Incoherence Speckle Reduction

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Solution Overview

Problem

Current lithographic processes face challenges in accurately measuring small pitch alignment marks and overlay errors due to interference artifacts like speckle effects from spatially coherent radiation, and existing alignment sensors require bright-field imaging to resolve small mark pitches, which is less effective than dark-field imaging.

Innovation Solution

A metrology device is developed to produce spatially incoherent illumination beams with mutual coherence between corresponding pupil points, allowing for dark-field imaging with minimal speckle artifacts, enabling accurate measurement of small pitch targets and overlay errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If spatially coherent radiation is used for illumination, then interference artifacts like speckle effects occur, but measurement precision deteriorates

Engineering Contradiction:

Improvealignment mark measurement accuracyVSAvoidspeckle effects

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent changes the coherence parameter of the illumination radiation from spatially coherent to spatially incoherent. This is achieved by using a multimode fiber to couple incoherent light from a halogen lamp into the optical path, fundamentally altering the radiation properties to eliminate speckle effects while maintaining measurement precision through incoherent imaging techniques

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If bright-field imaging is used to resolve small mark pitches, then measurement capability is improved, but imaging effectiveness deteriorates compared to dark-field imaging

Engineering Contradiction:

Improvesmall pitch target resolutionVSAvoidimaging effectiveness

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent inverts the traditional imaging approach by using dark-field imaging instead of bright-field imaging. The optical system is configured to detect only scattered light from the alignment marks rather than transmitted light, allowing small pitch targets to be resolved effectively. The incoherent illumination combined with dark-field detection provides superior contrast and resolution for small features

Inventive Principle:

Principle #13The other way round (Inversion)

3Manufacturing precision

If conventional alignment sensors are used, then overlay measurement is possible, but measurement accuracy deteriorates due to interference artifacts

Engineering Contradiction:

Improveoverlay measurement accuracyVSAvoidmeasurement robustness

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent converts the harmful effect of incoherent radiation into a beneficial property. By using spatially incoherent illumination, the system eliminates speckle effects and interference artifacts that plague conventional coherent systems. The incoherent nature of the light provides superior measurement robustness and accuracy for overlay measurements, turning what was previously a limitation into a significant advantage

Inventive Principle:

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

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

The metrology device achieves precise alignment and overlay measurements with reduced interference artifacts, improving the accuracy and robustness of position sensing and overlay metrology in lithographic processes.

Implementation Method 1

produce measurement illumination comprising a plurality of illumination beams, each of said illumination beams being spatially incoherent or pseudo-spatially incoherent

Methodology Applied

Scientific EffectSpatial incoherence: Interference

Implementation Method 2

each pupil point in each one of said plurality of illumination beams has a corresponding pupil point in at least one of the other illumination beams of said plurality of illumination beams thereby defining multiple sets of corresponding pupil points, and wherein the pupil points of each set of corresponding pupil points are spatially coherent with respect to each other

Methodology Applied

Scientific EffectMutual coherence: Interference

Implementation Method 3

a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured

Methodology Applied

Scientific EffectScattering: Scattering

Implementation Method 4

Diffraction-based overlay metrology using dark-field imaging of the diffraction orders enables overlay measurements on smaller targets

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentEP3853666B1Metrology sensor for position metrology

Publication Date: 2022.08.10 ASML NETHERLANDS BV

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AI summary

Disclosed is a metrology device (1600) configured to produce measurement illumination comprising a plurality of illumination beams, each of said illumination beams being spatially incoherent or pseudo-spatially incoherent and comprising multiple pupil points in an illumination pupil of the metrology device. Each pupil point in each one of said plurality of illumination beams has a corresponding pupil point in at least one of the other illumination beams of said plurality of illumination beams thereby defining multiple sets of corresponding pupil points, and the pupil points of each set of corresponding pupil points are spatially coherent with respect to each other.