Multi-Beam Microscopy Alignment Using Aberration Feedback
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Solution Overview
Problem
Multi-beam scanning electron microscopes face challenges in achieving high imaging quality due to aberrations caused by misalignment of optics, which cannot be corrected manually during sample scanning, leading to loss of image quality in large regions of interest.
Innovation Solution
A method to automatically align the optics of a multi-beam microscopy system by measuring the positions of multiple beamlets at the sample plane, determining coefficients for an aberration model, and adjusting the illuminator based on these coefficients to correct aberrations before or during image acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If manual alignment of optics is used in multi-beam system, then device complexity is reduced, but manufacturing precision deteriorates due to aberrations caused by misalignment
Solution Approach 1:
The system performs self-alignment by automatically measuring beamlet positions at the sample plane, calculating aberration coefficients, and adjusting the illuminator without manual intervention. The multi-beam system uses its own beamlets to detect positional deviations and corrects its own alignment errors through feedback control.
Solution Approach 2:
The alignment system implements a closed-loop feedback mechanism where beamlet positions are continuously measured, compared against ideal positions to determine aberration coefficients, and used to adjust the illuminator settings. This feedback loop eliminates misalignment aberrations by constantly correcting beam positions based on measured deviations.
2Productivity
If manual adjustments are made during sample scanning, then ease of operation is maintained, but productivity deteriorates due to loss of image quality in large regions of interest
Solution Approach 1:
The system automatically maintains alignment during sample scanning without requiring operator intervention. The illuminator adjusts itself based on real-time beamlet position measurements, allowing continuous high-speed imaging of large regions without manual re-alignment stops.
Solution Approach 2:
The system performs preliminary alignment correction by determining aberration coefficients and adjusting the illuminator before image acquisition begins or during scanning, ensuring optimal beam positions are maintained throughout the imaging process without interrupting productivity.
3Measurement precision
If aberrations are not corrected, then device complexity is minimized, but measurement precision deteriorates due to aberration-induced position errors
Solution Approach 1:
The system measures actual beamlet positions at the sample plane, compares them with ideal positions to calculate aberration coefficients, and uses this feedback to adjust the illuminator. This closed-loop measurement and correction process eliminates position errors caused by aberrations, achieving high measurement precision.
Solution Approach 2:
The system replaces complex mechanical realignment mechanisms with computational methods. Instead of physically adjusting optical components during scanning, the system calculates aberration coefficients from measured positions and applies computational corrections to the illuminator, simplifying the mechanical complexity while improving precision.
Data Source
AI summary
The beamlets in a multi-beam microscopy system are aligned based on coefficients of a fitted aberration model. In particular, an illuminator for directing the beamlets towards the sample is adjusted based on the coefficients to correct the aberrations. The coefficients are obtained based on measured beamlets' positions in the sample plane.