Tunable Spectral Filter for Photocathode Illumination

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Solution Overview

Problem

Current electron beam inspection systems have low throughput due to limited photocathode material selection based on available laser sources, rather than inspection performance, and lack suitable illumination at shorter wavelengths, restricting the use of materials with wider bandgaps and higher valence band spin split energies.

Innovation Solution

A high-brightness electron beam source incorporating a broadband illumination source and a tunable spectral filter to generate filtered illumination, allowing for adjustable photocathode emission and optimizing quantum efficiency and energy spread of electron beams, enabling the use of a wider array of photocathode materials.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If laser sources are used to illuminate photocathodes, then photocathode emission can be achieved, but the selection of photocathode materials is limited by the availability of suitable laser wavelengths

Engineering Contradiction:

Improvephotocathode material selectionVSAvoidinspection throughput

Core Design Contradiction:

Adaptability or versatilityVSProductivity

Solution Approach 1:

The patent changes the illumination parameter from fixed-wavelength laser sources to broadband light sources with tunable spectral filters, enabling continuous wavelength adjustment to match different photocathode materials' excitation spectra, thereby expanding material selection while maintaining high quantum efficiency for throughput

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The broadband illumination source with tunable spectral filter serves multiple functions: it can illuminate various photocathode materials with different bandgaps, provide optimized excitation wavelengths for each material, and maintain high inspection throughput, replacing the need for multiple specialized laser sources

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If available laser sources are used for illumination, then photocathode inspection can be performed, but inspection performance is compromised due to limited wavelength options

Engineering Contradiction:

Improveinspection performanceVSAvoidillumination wavelength range

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent transforms the illumination system from fixed wavelength (laser) to continuously tunable wavelength (broadband source with spectral filter), allowing precise matching of illumination wavelength to each photocathode material's excitation spectrum, thereby optimizing inspection performance across diverse materials

Inventive Principle:

Principle #35Parameter changes

3Reliability

If photocathode materials with wider bandgaps are used, then higher valence band spin split energies and improved performance can be achieved, but suitable illumination sources at shorter wavelengths are unavailable

Engineering Contradiction:

Improvephotocathode performanceVSAvoidillumination wavelength availability

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent extends the available illumination wavelength range to shorter wavelengths by using broadband light sources with spectral filters that can tune into the UV and visible ranges, enabling excitation of photocathode materials with wider bandgaps and higher valence band spin split energies for improved reliability

Inventive Principle:

Principle #35Parameter changes

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 approach improves photocathode performance, increases operational lifetime, and enhances inspection system throughput by providing tailored illumination for various materials, optimizing quantum efficiency and energy spread, and enabling the use of materials previously incompatible due to lack of suitable illumination sources.

Implementation Method 1

a photocathode configured to emit one or more electron beams in response to the filtered illumination

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS10840055B2System and method for photocathode illumination inspection

Publication Date: 2020.11.17 KLA CORP

AI summary

A high-brightness electron beam source is disclosed. The electron beam source may include a broadband illumination source configured to generate broadband illumination. A tunable spectral filter may be configured to filter the broadband illumination to provide filtered illumination having an excitation spectrum. The electron beam source may further include a photocathode configured to emit one or more electron beams in response to the filtered illumination, wherein emission from the photocathode is adjustable based on the excitation spectrum of the filtered illumination from the tunable spectral filter.