Multilevel Electronic Counting for Charged Particle Beam Signal Detection

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Solution Overview

Problem

Current charged particle beam apparatuses, such as scanning electron microscopes, face challenges in achieving high signal-to-noise ratios with low electron irradiation amounts, particularly under low acceleration conditions, due to variations in electronic counting methods and analog detection noise, which affect the accuracy and dynamic range of image signals.

Innovation Solution

A multilevel electronic counting process is implemented, utilizing a charged particle beam apparatus with a photoelectric conversion unit, analog-to-digital conversion, and an arithmetic unit that counts digital signals based on unit peak values, enabling precise measurement of signal amounts and improving signal processing accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the electron irradiation amount per pixel is increased to improve signal-to-noise ratio, then the detection accuracy is improved, but the sample damage and charging effects become more severe

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidsample damage and charging

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent segments the signal detection process into multiple discrete levels using pulse height discrimination. Instead of treating all signals uniformly, the system divides them into distinct amplitude levels that correspond to different numbers of emitted electrons, enabling accurate measurement with lower total electron doses.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the detection parameter from continuous analog signal amplitude to discrete digital count levels. By converting the analog signal into multi-level digital counts through pulse height discrimination, the system achieves high measurement precision while using fewer electrons, thereby reducing sample damage and charging effects.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If the acceleration voltage is reduced to minimize sample damage, then the spatial resolution is improved, but the signal-to-noise ratio deteriorates due to lower emission rates

Engineering Contradiction:

Improvespatial resolutionVSAvoidsignal-to-noise ratio

Core Design Contradiction:

Manufacturing precisionVSMeasurement precision

Solution Approach 1:

The patent replaces the conventional analog detection system with a digital counting system. By substituting the analog signal processing mechanism with digital pulse height discrimination and counting, the system overcomes the low signal-to-noise ratio problem inherent in low acceleration voltage conditions, enabling high spatial resolution imaging with improved signal detection accuracy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Area of stationary object

If the pixel size is reduced to increase the observation area, then the field of view is expanded, but the electron irradiation amount per pixel decreases leading to poor signal detection

Engineering Contradiction:

Improveobservation areaVSAvoidsignal detection accuracy

Core Design Contradiction:

Area of stationary objectVSMeasurement precision

Solution Approach 1:

The patent introduces dynamic signal processing through multilevel electronic counting that adapts to varying signal conditions. The system dynamically discriminates pulse heights and assigns digital counts based on signal amplitude, enabling accurate detection even when the electron irradiation amount per pixel is reduced due to smaller pixel sizes in expanded observation areas.

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

This approach enhances the signal-to-noise ratio and improves signal accuracy with reduced electron irradiation, effectively addressing the limitations of conventional methods by providing a more precise and stable detection of emitted electrons.

Implementation Method 1

a photoelectric conversion unit that converts the charged particles from the sample into photons and converts the photons into an analog electric signal

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Implementation Method 2

When the emitted electrons collide with the scintillator, photons are generated

Methodology Applied

Scientific EffectScintillation: Scintillation

Data Source

PatentUS10453648B2Charged particle bean device and information-processing device

Publication Date: 2019.10.22 HITACHI HIGH TECH CORP

AI summary

There is provided a charged particle beam apparatus capable of obtaining a high SN ratio with a small electron irradiation amount. The charged particle beam apparatus includes a charged particle detection device. The charged particle detection device detects an analog pulse waveform signal (110) in a detection of emitted electrons (1 event) when one primary electron enters a sample, converts the analog pulse waveform signal (110) into a digital signal (111), perform a wave height discrimination (112) with the use of a unit peak corresponding electron, and outputs the digital signal (111) as a multilevel count value.