SEM Charging Distortion via Time Constant Scanning

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Solution Overview

Problem

Scanning electron microscopes face challenges in acquiring stable images due to charging effects on insulator specimens, which cause distortion and make it difficult to measure true dimensions and shapes, as existing methods fail to account for temporal and spatial changes in the charged state and its impact on electron beam trajectories.

Innovation Solution

A scanning electron microscope equipped with an energy filter to discriminate electron energy levels, time constant extraction means to analyze temporal changes, and scanning order determination means to optimize the scanning order based on extracted time constants, ensuring reduced deflection of the electron beam and improved image stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional electron beam scanning is used on insulator specimens, then image acquisition is performed, but charging effects cause image distortion and make dimension measurement inaccurate

Engineering Contradiction:

Improvedimension measurement accuracyVSAvoidcharging effect

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The system performs preliminary measurement of the time constant characterizing charging behavior before actual observation. This preliminary action allows the system to pre-determine the optimal scanning order that accounts for charging effects, thereby improving measurement accuracy without adding complex hardware modifications.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system dynamically adjusts the scanning order based on the measured time constant. Instead of using a fixed scanning pattern, the scanning sequence is optimized in real-time according to the specimen's charging characteristics, allowing the system to adapt to different specimens and minimize charging-induced distortion.

Inventive Principle:

Principle #15Dynamics

2Reliability

If the electron beam scans the specimen in conventional order, then observation is performed, but temporal and spatial changes in charged state cause trajectory deflection and image instability

Engineering Contradiction:

Improveimage stabilityVSAvoidscanning control complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system uses feedback from the measured time constant to determine the optimal scanning order. By measuring the charging behavior and using this information to adjust the scanning sequence, the system creates a feedback loop that improves image stability while keeping the control mechanism manageable through automated calculation.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system changes the scanning parameters (scan order, scan direction, dwell time distribution) based on the measured time constant. By optimizing these parameters according to the specimen's charging characteristics, the system achieves stable images without requiring complex hardware modifications.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If standard scanning methods are used, then observation area is covered, but charging causes spatial potential changes that deflect electron trajectories and distort observed shapes

Engineering Contradiction:

Improveshape observation accuracyVSAvoidoperation simplicity

Core Design Contradiction:

Manufacturing precisionVSEase of operation

Solution Approach 1:

The system performs preliminary measurement of charging characteristics (time constant) before observation. This preliminary action enables the system to pre-calculate and set the optimal scanning order that minimizes charging effects, thereby improving shape observation accuracy without making the operation more complex for the user.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system automatically determines the optimal scanning order based on the measured time constant without requiring manual intervention. The automated calculation and selection of scanning parameters makes the process self-service oriented, maintaining ease of operation while achieving high precision in shape observation.

Inventive Principle:

Principle #25Self-service

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 allows for the determination of an optimal scanning order that minimizes the influence of charging, resulting in accurate and stable image acquisition by maximizing the distance between scan points and arranging them in triangular, rectangular, or hexagonal patterns, thereby reducing image distortion.

Implementation Method 1

an energy filter to discriminate electron energy levels

Methodology Applied

Scientific EffectEnergy filtering: Filter (physical)

Implementation Method 2

a scanning electron microscope that detects electrons emitted from a specimen under electron beam irradiation

Methodology Applied

Scientific EffectElectron beam interaction: Electron Beam

Data Source

PatentUS8274048B2Scanning electron microscope having time constant measurement capability

Publication Date: 2012.09.25 HITACHI HIGH TECH CORP

AI summary

In a scanning electron microscope, an optimum scanning method for reducing the amount of deflection of a primary electron beam and secondary electrons is determined to acquire stable images. An energy filter is used to discriminate between energy levels. The change in yield of obtained electrons is used to measure the variation in specimen potential. The time constant of charging created during electron beam irradiation is extracted. The scanning method is optimized based on the extracted time constant to reduce the distortion and magnification variation that appear in a SEM image.