SEM Backscattered Electron Detector Positioning for Low Voltage Separation
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Solution Overview
Problem
Conventional scanning electron microscopes face difficulties in selectively detecting secondary electrons and backscattered electrons at low accelerating voltages due to the retarding field causing them to have similar energy levels, making it challenging to separate and detect these electrons effectively, especially with low probe currents.
Innovation Solution
A scanning electron microscope design that includes an electron source, aperture, specimen holder, objective lens, deflection means, secondary electron detector, backscattered electron detector, and a cylindrical electron transport system, where the backscattered electron detector is positioned inside the electron transport means and electrically wired to match the potential of the acceleration tube, allowing for the separation of secondary and backscattered electrons based on their trajectories and energy levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a retarding field is applied to minimize aberration at low accelerating voltage, then observation resolution is improved, but secondary electrons and backscattered electrons cannot be detected separately because they are accelerated to similar energy levels
Solution Approach 1:
The patent divides the detection system into separate detection paths for secondary electrons and backscattered electrons. By positioning the backscattered electron detector inside the electron transport means at a specific location, the system segments the electron detection process, allowing simultaneous separate detection of both electron types without requiring energy differentiation through Wien filters or energy barriers.
Solution Approach 2:
The patent transitions from energy-based separation (using Wien filters or energy barriers) to spatial-based separation. By placing the backscattered electron detector inside the electron transport means and utilizing the medium angle range for detection, the system creates a new spatial dimension for electron separation, enabling detection based on emission angle and trajectory rather than energy level differences.
2Object-affected harmful factors
If conventional detection methods are used at low accelerating voltage, then electron beam damage to specimen is reduced, but detection efficiency and resolution deteriorate due to low probe currents
Solution Approach 1:
The patent performs preliminary action by positioning the backscattered electron detector inside the electron transport means before electrons reach the specimen. This allows the system to capture backscattered electrons at medium angles during their initial trajectory, maximizing detection efficiency before the electron beam interacts with and potentially damages the specimen.
Solution Approach 2:
The patent changes the detection parameter from energy-based filtering to angular-based detection. By utilizing the medium angle range for backscattered electron detection and positioning the detector inside the electron transport means, the system achieves high detection efficiency at low accelerating voltages without requiring high probe currents that would cause specimen damage.
3Difficulty of detecting and measuring
If energy barriers or Wien filters are provided to selectively detect electrons, then electron separation is achieved, but device complexity increases
Solution Approach 1:
The patent extracts the backscattered electron detection function from the conventional external detection path and places it inside the electron transport means. By taking out the backscattered electron detector and positioning it within the acceleration tube, the system eliminates the need for separate energy barriers or Wien filters, simplifying the overall device structure while maintaining effective electron separation capability.
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 the selective detection of backscattered and secondary electrons even at low accelerating voltages and low probe currents, enhancing the resolution and detection efficiency of scanning electron microscopes by utilizing the medium angle range for high-yield electron detection.
Implementation Method 1
an objective lens for converging the electron beam on a surface of the specimen
Implementation Method 2
an electron source for generating an electron beam to be used as a probe
Implementation Method 3
a backscattered electron detector for detecting backscattered electrons from the specimen
Data Source
AI summary
To provide a low acceleration scanning electron microscope that can discriminate and detect reflected electrons and secondary electrons even with a low probe current, this scanning electron microscope is provided with an electron gun (29), an aperture (26), a sample table (3), an electron optical system (4-1) for making an electron beam (31) converge on a sample (2), a deflection means (10), a secondary electron detector (8), a reflected electron detector (9), and a cylindrical electron transport means (5) in a position between the electron gun (29) and sample (2). The reflected electron detector (9) is provided within the electron transport means (5) and on a side further away from the electron gun (29) than the secondary electron detector (8) and the deflection means (10). The reception surface (9-1) of the reflected electron detector (9) is electrically wired so as to have the same potential as the electron transport means (5).