Reflective Diffractive EUV Filters for OOB Light Detection

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Traditional spectral filters used in EUV lithography systems absorb out-of-band (OOB) light, leading to limited use life and inability to measure OOB light, increasing system complexity and reducing data utility.

Innovation Solution

A reflective spectral filter using a diffraction grating-based system that separates EUV light and OOB light into different optical paths, allowing detection and measurement of OOB light while preserving EUV light for downstream use.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional absorptive spectral filters are used to suppress OOB light, then OOB light suppression is achieved, but the filter has limited use life due to absorption induced damage and cannot measure OOB light

Engineering Contradiction:

Improvefilter use lifeVSAvoidOOB light measurement capability

Core Design Contradiction:

ReliabilityVSLoss of information

Solution Approach 1:

The patent inverts the traditional absorptive filtering approach by using a reflective diffraction grating instead. Rather than absorbing OOB light, the grating reflects EUV light at a specific wavelength while directing OOB light to a separate detector, thereby extending filter life and enabling OOB light measurement simultaneously.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent introduces a diffraction grating as an intermediary element that separates EUV light from OOB light through diffraction. This mediator directs different wavelength ranges along different optical paths, allowing both suppression of OOB light in the EUV path and measurement of OOB light in a separate detection path.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If absorptive spectral filters are used to block OOB light, then spectral filtering is achieved, but system complexity increases and OOB light cannot be measured

Engineering Contradiction:

Improvespectral filtering effectivenessVSAvoidoptical system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The diffraction grating performs multiple functions simultaneously: it acts as a spectral filter to separate EUV light from OOB light, serves as a beam splitter to direct different wavelengths to different paths, and enables OOB light detection. This multi-functionality reduces the need for separate components, thereby managing system complexity while maintaining effective spectral filtering.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Object-affected harmful factors

If absorptive filters are used to suppress OOB light, then OOB light suppression is achieved, but the absorbed OOB light cannot be measured which reduces data utility

Engineering Contradiction:

ImproveOOB light suppressionVSAvoidOOB light data

Core Design Contradiction:

Object-affected harmful factorsVSLoss of information

Solution Approach 1:

The patent segments the optical path into two separate channels using the diffraction grating: one channel for EUV light that continues to the downstream optics, and another channel for OOB light that is directed to a dedicated detector. This segmentation allows simultaneous suppression of OOB light in the EUV path and measurement of OOB light intensity and characteristics in the separate detection path.

Inventive Principle:

Principle #1Segmentation

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 suppression and detection of OOB light, extending filter life and providing valuable data for system optimization.

Implementation Method 1

a binary grating having a preselected depth and preselected pitch configured to reflect spectrally filtered EUV light along a first optical path and reflect the OOB light along a second optical path

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

reflective spectral filter configured to receive the EUV illumination beam and spectrally filter the received EUV illumination beam by reflecting spectrically filtered EUV light along a first optical path and reflecting out-of-band (OOB) light along a second optical path

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS20250216254A1Diffractive EUV spectral purity filters for optical systems

Publication Date: 2025.07.03 KLA CORP

AI summary

A reflective imaging system disclosed herein includes an illumination source for generating a broad wavelength extreme ultraviolet (EUV) illumination beam, a reflective spectral filter for spectrally filtering the EUV illumination beam to direct spectrically filtered EUV light along a first optical path and reflect out-of-band (OOB) light along a second optical path, one or more detectors to detect the reflected spectrally filtered EUV light and OOB light, and a controller configured to obtain light data from the one or more detectors. The present disclosure further provides a method of spectrally filtering broad wavelength EUV light and embodiments of grating based EUV spectral filters.