Charged Particle Beam Aberration Mapping From Defocus Images
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Solution Overview
Problem
Existing charged particle beam systems, such as electron microscopes, face challenges in accurately determining and correcting beam aberrations, which limit the achievable resolution and require time-consuming measurements.
Innovation Solution
A method is developed to determine the actual values of beam aberration coefficients by simulating beam cross sections at different defocus settings for various aberration coefficient values, extracting relevant aberration characteristics, and establishing a dependency between the aberration coefficients and these characteristics, which can be used to correct the beam aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If aberration correction is applied to improve resolution, then the obtainable resolution is improved, but the complexity of adjusting aberration correctors increases due to the large number of controls and unknown beam aberration values
Solution Approach 1:
The patent changes the parameter representation from raw aberration coefficients to aberration invariants (Q1, Q2, Q3, Q4), which are derived through mathematical transformation of the original coefficients. This parameter transformation simplifies the adjustment process by reducing the number of independent controls needed while maintaining the ability to correct all aberration types. The invariants provide a more efficient parameter space for optimization.
Solution Approach 2:
The patent uses simulated beam cross sections as copies of actual beam behavior to establish reference data. By creating simulated images with known aberration coefficients and extracting aberration characteristics from these simulations, the system builds a reference library that can be compared against actual measurements, enabling automated determination of aberration values without manual adjustment of multiple controls.
2Measurement precision
If multiple measurements are carried out to determine aberration dependencies, then the accuracy of aberration determination is improved, but the time required for aberration correction increases
Solution Approach 1:
The patent performs preliminary simulations to establish the relationship between aberration coefficients and aberration characteristics before actual measurement. By pre-calculating beam cross sections for various aberration values and extracting characteristics from these simulations, the system creates a reference framework that enables rapid determination during actual operation, avoiding the need for multiple iterative measurements.
Solution Approach 2:
The patent replaces the mechanical/iterative measurement process with a computational approach. Instead of physically adjusting aberration correctors and taking multiple measurements to determine dependencies, the system uses computer simulations to calculate the relationships between aberration coefficients and observable characteristics, then applies these pre-determined relationships to actual data for rapid aberration determination.
3Reliability
If aberration correctors with many controls are used to compensate beam aberrations, then the correction capability is improved, but the ease of operation deteriorates due to the difficulty of appropriately adjusting the settings
Solution Approach 1:
The patent extracts the essential aberration information from the complex set of aberration coefficients by identifying and utilizing aberration invariants. These invariants (Q1, Q2, Q3, Q4) represent the core aberration characteristics that need to be corrected, allowing the system to focus adjustment efforts on the most significant parameters rather than manually tuning all possible controls.
Solution Approach 2:
The patent implements an automated feedback system that determines aberration coefficients by comparing extracted characteristics from actual beam images against simulated reference data. This feedback mechanism automatically identifies the correct aberration values and adjusts the corrector settings accordingly, eliminating the need for manual adjustment of multiple controls while maintaining high correction capability.
Data Source
AI summary
A method of determining aberrations of a charged particle beam (11) focused by a focusing lens (120) with a given numerical aperture (NA) toward a sample (10) in a charged particle beam system is described. The method includes: (a.) simulating, based at least on the given numerical aperture (NA), one or more beam cross sections at one or more first defocus settings for each of two or more different values of a first beam aberration coefficient (C1) of a set of beam aberration coefficients (C1 . . . n), to provide a plurality of first simulated beam cross sections; (b.) extracting two or more values of a first aberration characteristic (˜C1) that is related to the first beam aberration coefficient (C1) from the plurality of first simulated beam cross sections; (c.) determining a first dependency between the first beam aberration coefficient (C1) and the first aberration characteristic (˜C1); (d.) taking one or more images of the sample at the one or more first defocus settings or at one or more second defocus settings, to provide one or more taken images, and retrieving one or more retrieved beam cross sections from the one or more taken images; (e.) extracting a retrieved value of the first aberration characteristic from the one or more retrieved beam cross sections; and (f.) determining an actual value of the first beam aberration coefficient based on the first dependency and based on the retrieved value of the first aberration characteristic.