Photonic Crystal Fiber Mode Control for Stable Broadband Output

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Solution Overview

Problem

Existing broadband radiation sources for metrology applications in IC manufacturing suffer from issues such as high intensity instability and low spatial coherence, making them unsuitable for precise and consistent measurements.

Innovation Solution

A mode control system for a photonic crystal fiber (PCF) based broadband radiation source that includes a detection unit to measure radiation parameters and a processing unit to evaluate mode purity, generating a control signal for optimizing pump coupling conditions to stabilize the fundamental transverse mode (LP01) and enhance mode purity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If broadband radiation sources are used for metrology applications, then measurement robustness and accuracy are improved, but intensity instability and low spatial coherence occur

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidintensity stability

Core Design Contradiction:

Measurement precisionVSStability of the object's composition

Solution Approach 1:

The patent changes the spatial distribution parameters of the pump beam by dynamically adjusting coupling conditions (beam position, angle, focus) to optimize the excitation of the photonic crystal fiber, thereby stabilizing the broadband radiation output intensity while maintaining measurement accuracy

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements a feedback control system that monitors the output intensity of the broadband radiation source and dynamically adjusts the pump beam coupling conditions to maintain stable operation, resolving the intensity instability issue while preserving measurement precision

Inventive Principle:

Principle #23Feedback

2Reliability

If broadband radiation sources are used for metrology applications, then measurement robustness is improved, but spatial coherence is reduced

Engineering Contradiction:

Improvemeasurement robustnessVSAvoidspatial coherence

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent creates a localized high-coherence region at the fiber core by optimizing pump beam coupling, ensuring that the broadband radiation maintains sufficient spatial coherence for robust metrology measurements while still providing broad spectral coverage

Inventive Principle:

Principle #3Local quality

3Measurement precision

If pump coupling conditions are optimized for fundamental mode, then mode purity is improved, but power efficiency may be reduced

Engineering Contradiction:

Improvemode purityVSAvoidpower efficiency

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent dynamically adjusts pump coupling conditions to optimize for fundamental mode excitation, using real-time control of beam position, angle, and focus to maximize mode purity while maintaining acceptable power efficiency through adaptive optimization

Inventive Principle:

Principle #15Dynamics

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 achieves stable and high-coherence broadband radiation output, improving measurement accuracy and consistency in metrology tools by ensuring maximum power efficiency and minimizing higher-order mode losses.

Implementation Method 1

A method and apparatus for the generation of supercontinuum radiation in a photonic crystal fiber are described.

Methodology Applied

Scientific EffectSupercontinuum generation:

Implementation Method 2

The pump laser radiation is fed into a photonic crystal fiber, in which a nonlinear optical process transforms the pump laser radiation into broadband radiation.

Methodology Applied

Scientific EffectNonlinear optical process:

Implementation Method 3

at least one detection unit configured to measure one or more parameters of radiation emitted from the broadband radiation source to generate measurement data

Methodology Applied

Scientific EffectRadiation detection:

Data Source

PatentUS12386270B2Mode control of photonic crystal fiber based broadband radiation sources

Publication Date: 2025.08.12 ASML NETHERLANDS BV

AI summary

A mode control system and method for controlling an output mode of a broadband radiation source including a photonic crystal fiber (PCF). The mode control system includes at least one detection unit configured to measure one or more parameters of radiation emitted from the broadband radiation source to generate measurement data, and a processing unit configured to evaluate mode purity of the radiation emitted from the broadband radiation source, from the measurement data. Based on the evaluation, the mode control system is configured to generate a control signal for optimization of one or more pump coupling conditions of the broadband radiation source. The one or more pump coupling conditions relate to the coupling of a pump laser beam with respect to a fiber core of the photonic crystal fiber.