Primary Beam Scanning Apparatus Bit Depth Control
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Solution Overview
Problem
Existing primary beam scanning apparatuses, such as scanning electron microscopes, face limitations in achieving higher bit depth data due to the fixed resolution of analog-to-digital converters, which restricts the quality of secondary electron images.
Innovation Solution
The apparatus and method allow for controlling the scan rate of the primary beam, enabling the analog-to-digital converter to sample and convert signals, and then averaging the digital signal, thereby modifying the bit depth based on the scan rate, allowing for data with a higher bit depth than the converter's resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an A/D converter with higher resolution is used to obtain data of higher bit depth, then the bit depth of image data is improved, but the device complexity and cost increase
Solution Approach 1:
The patent changes the scan rate parameter of the primary beam to control the number of samples collected per pixel. By adjusting the scan rate, the system can vary the effective bit depth of the image data without changing the A/D converter's hardware resolution, thus resolving the contradiction between measurement precision and device complexity
Solution Approach 2:
The patent performs preliminary sampling of the analog signal at a higher rate than the final display requirement before converting to digital form. This preliminary action allows the A/D converter to capture more information than immediately needed, which is then processed to achieve higher effective bit depth without requiring a higher-resolution converter
2Productivity
If the scan rate of the primary beam is increased to improve productivity, then the data collection speed is improved, but the bit depth of the obtained data decreases
Solution Approach 1:
The patent dynamically adjusts the scan rate of the primary beam based on the desired bit depth. The scan rate is made variable rather than fixed, allowing the system to optimize between productivity and measurement precision by selecting appropriate scan rates for different imaging requirements
Solution Approach 2:
The patent uses periodic scanning of the primary beam across the specimen, where each pixel is illuminated multiple times at different periods. By controlling the number of periodic scans and averaging the collected signals, the system achieves higher bit depth while maintaining acceptable data collection speed through optimized scan patterns
Data Source
AI summary
There is provided a primary beam scanning apparatus capable of producing data having a bit depth higher than the resolution of an analog-to-digital converter. The primary beam scanning apparatus is capable of controlling a scan rate of a primary beam for scanning a specimen. The scanning apparatus includes a detector for detecting signals generated in response to irradiation of the specimen with the primary beam and providing an analog output signal, an analog-to-digital converter for sampling the analog signal and converting it into a digital signal, and an arithmetic section for averaging the digital signal.