EUV Optical Sensor Contamination Measurement for Lithography Cleaning

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Solution Overview

Problem

Contamination on optical sensors in lithographic apparatuses affects their performance, leading to inaccurate pattern alignment and reduced productivity due to the need for frequent cleaning, which disrupts the manufacturing process.

Innovation Solution

A method and apparatus that directly measure contamination on optical sensors by illuminating a pattern with EUV radiation, projecting the reflected radiation, and moving the sensor to detect intensity variations, allowing for precise determination of contamination levels and thickness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If cleaning is performed frequently to remove contamination on optical sensors, then sensor performance is maintained, but productivity decreases due to suspended exposure operations

Engineering Contradiction:

Improvesensor performanceVSAvoidexposure throughput

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system performs preliminary contamination measurement before cleaning is actually needed. By continuously monitoring contamination levels on optical sensors using EUV radiation intensity measurements, the system determines when contamination reaches thresholds that would affect sensor performance, and schedules cleaning operations only at those points, avoiding unnecessary cleaning interruptions.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system implements a feedback mechanism where contamination levels are measured by detecting intensity variations of EUV radiation passing through or reflecting off the sensor. This measurement feedback loop provides real-time information about contamination state, enabling condition-based cleaning decisions that maintain sensor performance while minimizing productivity loss from cleaning operations.

Inventive Principle:

Principle #23Feedback

2Productivity

If cleaning is delayed to maintain productivity, then exposure throughput is maintained, but sensor performance deteriorates due to contamination build-up

Engineering Contradiction:

Improveexposure throughputVSAvoidsensor performance

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The feedback mechanism continuously monitors contamination levels and provides real-time data on sensor degradation. This enables the system to delay cleaning only as long as performance thresholds are met, and to trigger cleaning operations precisely when contamination reaches critical levels, thereby maintaining productivity while preventing performance deterioration.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system changes the parameter being monitored from indirect estimates to direct contamination measurement using EUV radiation intensity. By measuring actual contamination levels rather than relying on time-based schedules or performance degradation symptoms, the system can optimize the balance between cleaning frequency and productivity maintenance.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If indirect estimation methods are used to monitor contamination, then measurement complexity is reduced, but measurement precision is insufficient for accurate cleaning timing

Engineering Contradiction:

Improvemeasurement system complexityVSAvoidcontamination level accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The system uses an intermediary substance (hydrocarbon contamination layer) that has predictable optical properties in the EUV range. By measuring the absorption or reflection characteristics of this intermediary layer, the system achieves precise contamination thickness measurement without requiring direct physical access to the sensor surface or complex measurement apparatus.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system replaces mechanical or direct physical measurement methods with optical measurement using EUV radiation. This substitution allows for non-contact, remote measurement of contamination levels with high precision, maintaining low system complexity while achieving accurate contamination thickness determination through optical property changes.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

Enables efficient cleaning only when necessary, reducing downtime and maintaining productivity by providing a straightforward and accurate measurement of contamination, thus improving the performance and efficiency of lithographic apparatuses.

Implementation Method 1

an intensity of EUV radiation measured by the optical sensor varies as a function of the position of the optical sensor

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Data Source

PatentUS20250277750A1Contamination measurement

Publication Date: 2025.09.04 ASML NETHERLANDS BV

AI summary

A method of determining contamination of an optical sensor in a lithographic apparatus, the method including projecting patterned reflected EUV radiation towards the optical sensor and thereby forming an aerial image of a pattern, moving the optical sensor relative to the patterned reflected EUV radiation such that an intensity of EUV radiation measured by the optical sensor varies as a function of the position of the optical sensor, wherein the intensity measured by the optical sensor passes through a minimum, and using the measured intensity to measure contamination of the optical sensor.