Scanning Method for SEM Image Coherence and Resolution
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Solution Overview
Problem
Existing scanning techniques, such as Scanning Electron Microscopy, face challenges in correcting for interference frequencies higher than the frame rate, leading to image blurring and poor signal-to-noise ratio due to mechanical vibrations and other interferences, especially with increasing image resolution, which requires costly structural shielding.
Innovation Solution
The method involves scanning a sample with two intersecting scan patterns at an angle, adjusting nominal scan positions using a weight factor based on temporal coherence to improve data similarity, and combining images to form an improved image, which can include interpolation for empty positions, using optimization techniques like Steepest Ascent Hill Climbing or Belief Propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a slow scan speed is used to achieve a high signal-to-noise ratio, then the signal-to-noise ratio is improved, but mechanical vibrations and interferences cause blurring and flagging in the image
Solution Approach 1:
The patent divides the scanning process into multiple independent scan patterns (e.g., raster scan and reverse raster scan) that are acquired separately and then combined. Each scan pattern is stored in a separate memory area, allowing independent processing and correction of interference effects before combination, thereby resolving the contradiction between signal-to-noise ratio and image sharpness.
Solution Approach 2:
The patent combines multiple scan patterns (first scan pattern and second scan pattern) into a single improved image. By merging data from multiple scans with different interference characteristics, the method achieves both high signal-to-noise ratio and sharp image quality, as the combination process allows for correction of blurring and flagging artifacts.
2Manufacturing precision
If a fast scan speed (TV-rate) is used to reduce the effect of interferences, then image sharpness is improved, but the signal-to-noise ratio becomes very poor
Solution Approach 1:
The patent employs periodic scanning with multiple scan patterns acquired in sequence. By performing repeated scans with different patterns and combining them, the method accumulates signal information over time (improving signal-to-noise ratio) while maintaining the sharpness benefits of fast scanning through the periodic acquisition and combination process.
3Manufacturing precision
If multiple scan patterns are combined to correct for drift, then image quality is improved, but the processing complexity and time required for correction increases
Solution Approach 1:
The patent performs preliminary processing by storing each scan pattern in a separate memory area associated with its specific scan pattern type. This preliminary organization allows for efficient subsequent processing where drift correction and combination can be performed systematically without excessive computational overhead, reducing the overall processing time while maintaining image quality.
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 effectively reduces interference effects, improving image coherence and resolution while reducing the need for costly shielding measures, by adjusting scan positions to maximize data similarity and combining images efficiently.
Implementation Method 1
In a SEM a sample is scanned with a probe in the form of a focused beam of electrons
Implementation Method 2
In response to said scanning radiation emerges from the sample, such as secondary electrons (SE's)
Implementation Method 3
backscattered electrons (BSE's)
Data Source
AI summary
The method relates to a method of scanning a sample. Scanning a sample is typically done by scanning the sample with a probe along a multitude of parallel lines. In prior art scan methods a sample is scanned multiple times with a nominally identical scan pattern. The invention is based on the insight that the coherence between adjacent points in a direction along the scan direction is much better than the coherence of adjacent points perpendicular to the scan direction. By combining two images that are scanned perpendicular to each other, it should thus be possible to form an image making use of the improved coherence (due to shorter temporal distance) in both directions. The method thus involves scanning the sample with two scan patterns, the lines of one scan pattern preferably perpendicular to the lines of the other scan pattern. Hereby it is possible to use the temporal coherence of scan points on a line of one scan pattern to align the lines of the other scan pattern, and vice versa.