STEM Aberration Correction via Auto-Correlation Segmentation
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Solution Overview
Problem
Existing aberration correction methods for scanning transmission electron microscopes (STEM) fail to accurately correct aberrations, especially when dealing with specimens like the dumbbell structure in Si [110], due to the auto-correlation function reflecting both the electron beam intensity distribution and specimen structure, leading to incorrect aberration calculations.
Innovation Solution
The method involves acquiring two STEM images at different defocus amounts, calculating their auto-correlation functions, and fitting aberration functions to intensity profiles at inflection points to obtain accurate aberration coefficients, independent of the specimen structure, allowing for precise aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If the auto-correlation function of a STEM image is used for aberration correction, then the aberration can be measured automatically, but the specimen structure is reflected on the auto-correlation function leading to incorrect aberration calculations
Solution Approach 1:
The patent segments the auto-correlation function analysis by focusing only on the central region (within a predetermined distance from the center) and excluding regions affected by specimen structure. This segmentation allows automatic processing while avoiding contamination from specimen features, thereby resolving the contradiction between automation and measurement accuracy.
2Ease of operation
If aberration correction is performed using STEM images of specimens with specific structures (e.g., dumbbell structure), then the process is simplified, but the calculation result indicates the presence of aberration even when there is no aberration
Solution Approach 1:
The patent applies local quality by differentiating the treatment of different regions in the auto-correlation function. The central region is used for aberration measurement while peripheral regions are excluded. This localized approach maintains operational simplicity while ensuring reliability by avoiding regions where specimen structure causes false aberration signals.
3Quantity of substance
If the entire auto-correlation function is used for aberration fitting, then more data is available for calculation, but specimen structure effects contaminate the aberration coefficient calculation
Solution Approach 1:
The patent extracts only the useful portion of the auto-correlation function (the central region within predetermined distance from center) and excludes the contaminated peripheral regions. This extraction maintains sufficient data quantity for accurate fitting while removing specimen structure effects, thereby resolving the contradiction between data quantity and measurement precision.
Data Source
AI summary
In a scanning transmission electron microscope, a control unit performs: processing of calculating a first auto-correlation function that is an auto-correlation function of a first scanning transmission electron microscope image; processing of acquiring a first intensity profile along a straight line that passes through a center of the first auto-correlation function; processing of obtaining a position of an inflection point that is closest to the center of the first auto-correlation function in the first intensity profile and adopting an intensity at the position as a first reference intensity; processing of obtaining an aberration coefficient by fitting a first aberration function to an isointensity line that connects positions where intensity is equal to the first reference intensity in the first auto-correlation function and by fitting a second aberration function to an isointensity line that connects positions where intensity is equal to a second reference intensity in a second auto-correlation function; and processing of controlling an electron optical system based on the aberration coefficient.