Optical Isolator Layout for EUV Back Reflection Rejection

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Solution Overview

Problem

Existing optical systems for extreme ultraviolet (EUV) light sources face challenges in effectively isolating back reflections, which can lead to reduced optical power delivery to the target and instability in EUV light production.

Innovation Solution

The implementation of an optical isolator comprising a plurality of dichroic optical elements and an acousto-optic modulator, which separates and deflects back reflections away from the light source, thereby preventing them from entering the light-generation module.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional optical isolation methods are used, then the system structure is simple, but back reflections are not effectively isolated, leading to reduced optical power delivery and instability in EUV light production

Engineering Contradiction:

Improvestability of EUV light productionVSAvoidcomplexity of optical isolator

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The optical isolator is divided into multiple functional segments: dichroic optical elements for wavelength-selective reflection, acousto-optic modulators for directional deflection control, and polarizing elements for polarization-based isolation. Each segment performs a specific isolation function, collectively achieving comprehensive back reflection rejection while maintaining system reliability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Acousto-optic modulators serve as intermediary devices between the incoming light and the optical amplifier. These modulators use acoustic waves to create dynamic diffraction gratings that deflect back reflections away from the amplifier when acoustic signals are applied, while allowing forward-propagating light to pass through undisturbed when acoustic signals are absent

Inventive Principle:

Principle #24Intermediary (Mediator)

2Power

If back reflections are allowed to enter the light-generation module, then the optical system is simpler, but optical power delivery to the target is reduced

Engineering Contradiction:

Improveoptical power deliveryVSAvoidcomplexity of optical isolation system

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

The system converts potentially harmful back reflections into a controllable optical path. By using dichroic elements to reflect specific wavelengths and acousto-optic modulators to deflect these reflections away from the amplifier, the harmful back reflections are transformed into a manageable optical component that can be routed elsewhere, thereby protecting optical power delivery

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The optical isolator employs dynamically controllable acousto-optic modulators that can switch between transmitting and deflecting states based on acoustic signal application. This dynamic control allows the system to adaptively manage optical paths, ensuring maximum power delivery to the target while actively preventing back reflections from entering the amplifier

Inventive Principle:

Principle #15Dynamics

3Productivity

If back reflections enter the amplifier, then the system is simpler, but self-lasing increases and EUV light output decreases

Engineering Contradiction:

ImproveEUV light outputVSAvoidcomplexity of optical isolator

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The optical isolator implements preliminary anti-action by proactively blocking back reflections before they can enter the amplifier and cause self-lasing. The dichroic elements and acousto-optic modulators are positioned and configured to intercept and deflect reflected light paths, preventing the formation of feedback loops that would lead to self-lasing and reduce EUV light output

Inventive Principle:

Principle #9Preliminary anti-action

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 solution enhances the delivery of optical power to the target, increases the stability and efficiency of EUV light production, and reduces self-lasing, resulting in a higher average EUV light output.

Implementation Method 1

an optical modulator between two of the dichroic optical elements... the acousto-optic modulator can be configured to transmit the received light when the received light propagates in a first direction relative to the acousto-optic modulator and to deflect the received light away from the beam path when the received light propagates in a second direction relative to the acousto-optic modulator

Methodology Applied

Scientific EffectAcousto-optic effect: Acousto-optic Effect

Implementation Method 2

Each of the dichroic optical elements can be configured to reflect light having the first wavelength and to transmit light having the second wavelength

Methodology Applied

Scientific EffectDichroic reflection: Dichroic Filter

Data Source

PatentUS12245350B2Optical isolation module

Publication Date: 2025.03.04 ASML NETHERLANDS BV

AI summary

An optical source for a photolithography tool includes a source configured to emit a first beam of light and a second beam of light, the first beam of light having a first wavelength, and the second beam of light having a second wavelength, the first and second wavelengths being different; an amplifier configured to amplify the first beam of light and the second beam of light to produce, respectively, a first amplified light beam and a second amplified light beam; and an optical isolator between the source and the amplifier, the optical isolator including: a plurality of dichroic optical elements, and an optical modulator between two of the dichroic optical elements.