Scanning Transmission Microscope Calibration via Beam Pattern
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Solution Overview
Problem
Current calibration methods for Scanning Transmission Charged-Particle Microscopes (STCPMs) face challenges in accuracy due to scaling issues and drift effects, particularly when transitioning between high and low magnification ranges, and are limited by the use of calibration specimens like cross gratings and crystalline samples.
Innovation Solution
A two-step calibration method involving a calibration specimen in non-scanning mode to accurately calibrate the detector's field of view, followed by recording a beam pattern in scanning mode to derive geometric aspects, which are then used to quantify and correct for distortions, thereby mitigating drift and scaling errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If calibration is performed using conventional methods with calibration specimens like cross gratings and crystalline samples, then calibration can be completed, but accuracy deteriorates due to scaling issues and drift effects when transitioning between high and low magnification ranges
Solution Approach 1:
The patent introduces a beam pattern as an intermediary calibration target that is insensitive to drift effects. Instead of directly calibrating across magnification ranges using conventional specimens that suffer from drift and scaling issues, the method uses a drift-insensitive beam pattern recorded in scanning mode as a mediator. This beam pattern serves as a stable reference that connects the high-magnification non-scanning calibration domain to the low-magnification scanning domain, eliminating the reliability problems associated with conventional calibration specimens.
Solution Approach 2:
The patent changes the calibration approach by switching between two operational modes: non-scanning mode for high-magnification calibration of the detector's field of view, and scanning mode for recording the beam pattern. By changing operational parameters (scanning vs. non-scanning mode) and using the known geometry of the beam pattern, the method achieves accurate calibration across magnification ranges without suffering from drift effects that plague conventional single-mode calibration approaches.
2Device complexity
If a single calibration method is used for both high and low magnification ranges, then the calibration process is simplified, but measurement precision deteriorates due to drift effects and scaling issues
Solution Approach 1:
The patent segments the calibration process into two distinct parts: (1) non-scanning mode calibration for determining the detector's field of view at high magnification, and (2) scanning mode calibration for recording the beam pattern and deriving geometric aspects. This segmentation allows each part to be optimized for its specific purpose, achieving high precision without requiring a complex unified calibration method. The two-step approach is simpler than attempting to create a single method that handles all magnification ranges with equal precision.
3Ease of manufacture
If conventional calibration specimens like cross gratings are used, then calibration can be performed, but accuracy deteriorates due to inherent limitations of these specimens
Solution Approach 1:
Instead of using physical calibration specimens like cross gratings that have inherent manufacturing limitations and drift issues, the patent creates a virtual calibration target by recording the beam pattern in scanning mode. This copied representation of the beam pattern serves as the calibration reference, eliminating the need for physical specimens with their associated accuracy limitations. The beam pattern copy is drift-insensitive and can be recorded with high precision, thereby improving calibration accuracy while maintaining ease of implementation.
Data Source
Figure 1
Figure 2A~2B
AI summary
A method of calibrating a Scanning Transmission Charged-Particle Microscope comprising: - A specimen holder, for holding a specimen; - A source, for producing a beam of charged particles; - An illuminator, for directing said beam so as to irradiate the specimen; - An imaging system, for directing charged particles that traverse the specimen onto a detector; - Scanning means, for causing said beam to undergo scanning motion relative to a surface of the specimen, which microscope can be operated in: - A non-scanning mode, whereby said beam is relatively broad and said detector forms an image without invocation of said scanning means; or - A scanning mode, whereby said beam is relatively narrow and said detector accumulates an image as a function of scan position of said beam, which method comprises the following steps: - Providing a calibration specimen on said specimen holder; - In non-scanning mode, using said detector to form a calibration image of the calibration specimen, using a given configuration of said imaging system; - Utilizing a known dimension of said calibration specimen and comparing it to a corresponding dimension in said calibration image to calibrate a characteristic dimension of a field of view of said detector; - In scanning mode, recording a beam pattern of said beam in the calibrated field of view of said detector, and examining the recorded beam pattern to derive a geometric aspect thereof.