Immersion Optical Review for High-Resolution Wafer Defect Classification

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Solution Overview

Problem

Current optical review methods for semiconductor manufacturing, such as those using dry, digitized microscopes and scanning electron microscopy, are inadequate for detecting and classifying defects in advanced wafer level packages (aWLP) due to physical limitations in wavelength and numerical aperture, and can damage wafers, being costly and inefficient.

Innovation Solution

An optical review system employing immersion technology, differential phase contrast, focus scan, polarization control, and UV/DUV wavelengths, combined with a processor for generating intensity and phase images, to enhance defect detection and classification in aWLP and backend wafers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If UV or DUV wavelengths are used for high-resolution imaging, then measurement precision is improved, but object-affected harmful factors worsen due to wafer damage

Engineering Contradiction:

Improveimage qualityVSAvoidwafer damage

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The system changes the wavelength parameter from UV/DUV to visible range, and adjusts the numerical aperture parameter (NA ≤ 1.0) to achieve optimal resolution without causing wafer damage. This parameter optimization allows sufficient image quality for defect detection while avoiding the harmful effects of higher energy wavelengths.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If scanning electron microscopy is used for defect detection, then measurement precision is improved, but productivity worsens due to slow inspection speed

Engineering Contradiction:

Improvedefect detection capabilityVSAvoidinspection speed

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The system replaces the mechanical electron beam scanning mechanism with an optical imaging system using visible light and high numerical aperture objectives. This substitution maintains defect detection capability while dramatically improving inspection speed and productivity, as optical systems can capture images much faster than sequential electron beam scanning.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If scanning electron microscopy is used for defect detection, then measurement precision is improved, but device complexity worsens due to vacuum compatibility requirements

Engineering Contradiction:

Improvedefect detection capabilityVSAvoidvacuum system requirements

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system replaces the vacuum-based electron microscopy mechanism with an optical system operating in ambient conditions. This eliminates the need for complex vacuum chambers, electrostatic chucks, and vacuum-compatible materials, significantly reducing device complexity while maintaining defect detection capability for aWLP and backend wafers.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Measurement precision

If high numerical aperture is used for imaging, then measurement precision is improved, but device complexity worsens due to optical system limitations

Engineering Contradiction:

Improveimage qualityVSAvoidoptical system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system optimizes the numerical aperture parameter to NA ≤ 1.0, which provides sufficient resolution for defects at 1 μm and 0.4 μm design rules without requiring overly complex optical systems. This parameter selection balances measurement precision with manageable device complexity, avoiding the need for extremely high NA objectives that would increase system complexity.

Inventive Principle:

Principle #35Parameter changes

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 system provides high-resolution, non-destructive defect review and classification, balancing performance, speed, and cost, suitable for defects ranging from 0.2 µm to 1 µm, while avoiding UV/DUV damage and vacuum compatibility issues.

Implementation Method 1

the light source includes a white light source that emits ultraviolet or deep ultraviolet wavelengths

Methodology Applied

Scientific EffectUltraviolet emission:

Implementation Method 2

an immersion objective that uses a fluid having a refractive index greater than 1.5

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 3

the light source includes a plurality of light-emitting diodes configured to form illumination patterns for differential phase contrast

Methodology Applied

Scientific EffectPhase contrast:

Data Source

PatentEP4121747B1Systems and methods of high-resolution review for semiconductor inspection in backend and wafer level packaging

Publication Date: 2026.02.18 KLA CORP

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AI summary

A review system and operation method directs a beam of light toward a sample on a stage. The sample is a wafer level packaging wafer or a backend wafer. Defect review is performed based on the light reflected from the sample. The review system can use one or more of: a fluid supplied by an immersion subsystem that includes a fluid supply unit and a fluid removal unit; an illumination pattern for differential phase contrast; or ultraviolet or deep ultraviolet wavelengths.