Complementary Plate Astigmatism for Semiconductor Height Sensor Resolution

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Solution Overview

Problem

Current semiconductor wafer inspection and metrology techniques, such as triangulation, geometric shadow, confocal microscopy, and white-light interferometry, lack accuracy and cost-effectiveness, especially for structures smaller than 10 μm and in mid-end-of-line (MEOL) and back-end-of-line (BEOL) applications.

Innovation Solution

A system and method utilizing a complementary plate with a beam splitter to create astigmatism and remove chromatic aberration, combined with a sensor and processor to determine the height of structures on a wafer, providing improved lateral resolution and sensitivity while maintaining cost-effectiveness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If existing triangulation and geometric shadow techniques are used, then the inspection process is simple and cost-effective, but the accuracy and precision are insufficient for structures smaller than 10 μm

Engineering Contradiction:

ImproveaccuracyVSAvoidcomplexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The optical path is segmented into multiple paths using beam splitters, with light directed to different detectors (photodiodes) based on the focal plane position. This segmentation allows simultaneous measurement of different depth information, improving accuracy for small structures while maintaining a manageable system architecture.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A complementary plate is introduced as an intermediary optical element to correct chromatic aberration introduced by the beam splitter. This intermediary component enables the system to achieve high measurement precision by compensating for optical distortions without requiring complete system redesign.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If confocal and interferometry methods are used, then the measurement accuracy is improved, but the throughput is reduced and cost increases

Engineering Contradiction:

ImproveaccuracyVSAvoidthroughput

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The system uses periodic scanning of the focal plane through controlled deflection, allowing sequential measurement of different depth layers. This periodic action enables accurate 3D measurement while maintaining higher throughput compared to traditional confocal methods by efficiently utilizing light paths and detectors.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The optical system is designed with multi-functionality, where the same optical path and detectors serve multiple measurement purposes (different depth planes, different spatial locations). This universality allows the system to achieve confocal-level accuracy without the throughput penalties of traditional confocal microscopy.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If beam splitter is used to create astigmatism for height detection, then the lateral resolution is improved, but chromatic aberration is introduced that degrades measurement accuracy

Engineering Contradiction:

Improvelateral resolutionVSAvoidchromatic aberration

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The complementary plate acts as an optical counterweight that compensates for the chromatic aberration introduced by the beam splitter. By introducing equal and opposite optical path differences, the system eliminates the harmful chromatic effects while preserving the beneficial astigmatism for height detection and lateral resolution.

Inventive Principle:

Principle #8Anti-weight (Counterweight)

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 solution enables fast and cost-effective 3D inspection and metrology with enhanced accuracy for semiconductor wafers, addressing the limitations of existing techniques by optimizing lateral resolution and sensitivity, and providing better throughput and precision for MEOL/BEOL applications.

Implementation Method 1

the beam splitter and the complementary plate can be used to create the desired astigmatism

Methodology Applied

Scientific EffectAstigmatism:

Implementation Method 2

the beam splitter and the complementary plate can be used to remove chromatic aberration

Methodology Applied

Scientific EffectChromatic aberration:

Implementation Method 3

A height sensor can then be used to determine a height of a structure on the wafer

Methodology Applied

Scientific EffectFocusing: Focusing

Implementation Method 4

The two photodiodes can receive different quantities of the light reflected from the wafer when the light reflected from the wafer is under-focused or over-focused

Methodology Applied

Scientific EffectPhotoelectric detection: Photoelectric Effect

Data Source

PatentUS10088298B2Method of improving lateral resolution for height sensor using differential detection technology for semiconductor inspection and metrology

Publication Date: 2018.10.02 KLA CORP

AI summary

A system that can be used for semiconductor height inspection and metrology includes a complementary plate that is used with a beam splitter to create desired astigmatism and to remove chromatic aberration. Simultaneous optimization of lateral resolution and sensitivity can be enabled. The complementary plate can be made of the same material and have the same thickness as the beam splitter.