Aperture Stop for Low Angle Dark Field Defect Detection

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Solution Overview

Problem

Conventional dark field defect detection techniques fail to enhance defects characterized by local low angle inclination on wafers, such as cracks and stresses, due to their reliance on large oblique angle illumination.

Innovation Solution

An aperture stop with a circular or non-circular region, featuring multiple opaque and opening points, is positioned at the objective lens to modify the illumination, allowing low angle specular reflections to pass through while blocking specular reflections from flat surfaces, effectively creating a low angle dark field illumination for defect detection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If large oblique angle illumination is used for dark field defect detection, then sensitivity to scratches and topography defects is improved, but detection capability for low angle inclination defects (cracks and stresses) deteriorates

Engineering Contradiction:

Improvedefect detection sensitivityVSAvoiddefect type coverage

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The aperture stop is divided into multiple independent opening regions, each corresponding to a specific illumination angle. This segmentation allows selective illumination at different angles to target different defect types, resolving the contradiction between optimizing for scratches (large angles) and cracks/stresses (low angles).

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system enables dynamic switching between different illumination angles by activating specific opening regions in the aperture stop. This dynamic capability allows the inspection system to adapt to different defect types and inspection requirements, improving both sensitivity and versatility.

Inventive Principle:

Principle #15Dynamics

2Illumination intensity

If conventional dark field illumination is used, then scattered light from scratches is enhanced, but low angle specular reflections from cracks and stresses are suppressed

Engineering Contradiction:

Improvescattered light collectionVSAvoidlow angle defect signal

Core Design Contradiction:

Illumination intensityVSLoss of information

Solution Approach 1:

Different regions of the aperture stop provide different illumination qualities - some regions provide large oblique angles for scratch detection, while other regions provide low angles for crack and stress detection. This local differentiation resolves the contradiction by ensuring each defect type receives optimized illumination.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The system changes the illumination angle parameter by selectively opening different regions of the aperture stop. This parameter adjustment allows optimization of the illumination angle to match the specific defect type being inspected, preventing information loss for low angle defects while maintaining scattered light collection capability.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If aperture stop with multiple opening regions is used, then defect detection versatility is improved, but device complexity increases

Engineering Contradiction:

Improvedefect type coverageVSAvoidaperture stop structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The aperture stop with multiple opening regions serves multiple functions simultaneously - it can detect scratches, cracks, stresses, and other defect types using a single component. This multi-functionality improves versatility without requiring multiple separate inspection systems, thereby limiting the increase in overall device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 configuration enhances the visibility of low angle surface tilts, leading to high contrast detection of defects like cracks and stresses, while minimizing reflection from flat regions, thereby improving defect detection sensitivity.

Implementation Method 1

blocking specular reflections from flat surfaces, effectively creating a low angle dark field illumination for defect detection

Methodology Applied

Scientific EffectSpecular reflection: Reflection

Implementation Method 2

dark field, which is designed to collect scattered light and is therefore sensitive to the wafer topography

Methodology Applied

Scientific EffectScattered light: Scattering

Data Source

PatentUS10222517B2Aperture stop

Publication Date: 2019.03.05 CAMTEK LTD

AI summary

An aperture stop that includes a non-circular region that comprises at least one opaque region and at least one opening region; wherein each point in the at least one opening region is (a) mapped to an angle of illumination and (b) is associated with a corresponding point in the at least one opaque region that. mapped to an angle of specular reflectance from the angle of illumination mapped to the opening point.