Charged Particle Beam Signal Detection with Pulse Counting
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Solution Overview
Problem
In charged particle beam apparatuses, high-speed scanning of fine patterns leads to reduced detection frequency of secondary electrons, resulting in low signal-to-noise ratios and reduced accuracy due to ringing pulses in analog detection systems, which obstruct efficient detection of low-amplitude signals, especially when observing deep-hole patterns.
Innovation Solution
A charged particle beam apparatus with a secondary electronic signal detection unit that includes both analog processing and pulse-count processing units, featuring a ringing pulse removal unit to eliminate ringing pulses and improve signal accuracy, enabling high-resolution imaging of fine patterns and deep-hole patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-speed scanning is performed to measure fine patterns, then productivity is improved, but measurement precision deteriorates due to reduced detection frequency and low signal-to-noise ratio
Solution Approach 1:
The detection system is segmented into multiple independent detection units (first detection unit and second detection unit), each processing signals from different charge particle types separately. This allows parallel processing of multiple signals without mutual interference, enabling high-speed scanning while maintaining detection precision through dedicated signal processing paths.
Solution Approach 2:
The patent applies pulse counting method selectively to backscattered electron signals (which have higher amplitude and less noise) while using analog integration for secondary electron signals (which have lower amplitude). This partial application of different processing methods optimizes the overall signal-to-noise ratio while maintaining high scanning speed.
2Ease of operation
If analog detection method is used to process signals, then ease of operation is improved, but measurement precision deteriorates due to ringing pulses obstructing low-amplitude signal detection
Solution Approach 1:
The signal processing system is divided into separate processing paths: one for secondary electrons using analog integration and another for backscattered electrons using pulse counting. This segmentation allows each path to use the most appropriate method for its signal characteristics, eliminating ringing pulse interference in the pulse counting path while maintaining operational simplicity.
Solution Approach 2:
A signal discrimination mechanism acts as an intermediary to classify incoming signals by type (secondary electron or backscattered electron) and route them to appropriate processing units. This intermediary function enables the system to automatically apply the correct processing method based on signal characteristics, improving precision without complicating user operation.
3Measurement precision
If pulse counting method is used to improve signal-to-noise ratio, then measurement precision is improved, but device complexity increases due to need for signal discrimination
Solution Approach 1:
The detection system is divided into separate detection units for different charge particle types, with each unit having dedicated processing circuitry. This segmentation eliminates the need for complex signal discrimination logic by providing separate processing paths, thereby reducing overall system complexity while maintaining high signal-to-noise ratio through pulse counting where applicable.
4Productivity
If scanning speed is increased to improve productivity, then productivity is improved, but measurement precision deteriorates due to reduced secondary electron detection frequency
Solution Approach 1:
The patent combines multiple detection methods (analog integration and pulse counting) and multiple detection units into a unified detection system. By merging the strengths of different detection approaches and processing multiple signal types simultaneously, the system maintains high measurement precision even at high scanning speeds where secondary electron detection frequency is reduced.
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
Enhances detection accuracy of high-speed and weak pulse signals, improving resolution and visibility of fine patterns and deep-hole features by removing ringing pulses and maintaining high signal-to-noise ratios.
Implementation Method 1
a scintillator and a photomultiplier tube are used in combination in order to detect secondary electrons and back scattered electrons which are generated when the sample has been irradiated with electron beams. When light emitted from the scintillator is incident upon the photomultiplier tube, a photoelectron is emitted from a photoelectric surface
Implementation Method 2
a photoelectron is emitted from a photoelectric surface and the photoelectron is multiplied by the photomultiplier tube
Data Source
AI summary
In an image forming method of charged particle beam apparatus for scanning a sample by irradiating the sample with a converged charged particle beam and detecting secondary charged particles generated from the sample by a detection unit, receiving and processing an output signal from the detection unit, and receiving the processed signal and forming an image of the sample, receiving and processing the output signal are performed by analogically processing the output signal and by performing pulse-count processing on the output signal, and pulse-count processing is performed by removing a ringing pulse in the output signal and counting pulses in the signal from which the ringing pulse has been removed.