Charged Particle Beam Axial Alignment via Astigmatism Cancellation
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Solution Overview
Problem
Current charged particle beam systems with multiple stages of multipole elements face difficulties in axial alignment due to the complexity of identifying and correcting aberrations, particularly six-fold astigmatism, which limits spatial resolution and increases alignment time.
Innovation Solution
The method involves producing astigmatic fields by multiple stages of multipole elements and using deflectors to cancel out astigmatisms of the same order, allowing for simultaneous alignment of the charged particle beam by controlling parts of its orbit perpendicular to the optical axis, thereby simplifying the alignment process and reducing the time required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If three or more stages of multipole elements are used to correct higher-order spherical aberration, then spatial resolution is improved, but the complexity of axial alignment increases and alignment time is extended
Solution Approach 1:
The patent divides the alignment process into two independent segments: (1) alignment of the first multipole element using conventional methods, and (2) alignment of the second and subsequent multipole elements using the newly invented method based on five-fold astigmatism cancellation. This segmentation allows each stage to be aligned independently without compounding complexity, resolving the technical contradiction by maintaining high spatial resolution while managing alignment complexity through process decomposition.
Solution Approach 2:
The patent introduces an intermediary diagnostic approach by using five-fold astigmatism as a specific indicator that uniquely identifies misalignment in the second and subsequent multipole elements. This intermediary marker serves as a clear signal that distinguishes alignment issues in later stages from those in the first stage, enabling targeted correction without requiring complex analysis of multiple aberration types simultaneously.
2Manufacturing precision
If conventional axial alignment methods are used with three or more stages of multipole elements, then alignment can be achieved, but the time required for alignment increases significantly
Solution Approach 1:
The patent applies preliminary action by first aligning the initial multipole element using conventional methods before applying the new alignment technique to subsequent elements. This sequential preliminary alignment establishes a reference point that simplifies the alignment of remaining elements, reducing the total alignment time while maintaining accuracy through a structured two-phase approach.
Solution Approach 2:
The patent changes the diagnostic parameter from general aberration analysis to specifically monitoring five-fold astigmatism for the second and subsequent multipole elements. This parameter change provides a more direct and sensitive indicator of alignment status, enabling faster detection and correction of misalignment without requiring time-consuming analysis of multiple aberration parameters.
3Manufacturing precision
If multiple stages of multipole elements are used to correct spherical aberration, then spatial resolution is improved, but six-fold astigmatism remains as a limiting factor
Solution Approach 1:
The patent converts the harmful effect of five-fold astigmatism (which arises from misalignment) into a beneficial diagnostic tool. By deliberately monitoring and using five-fold astigmatism as an alignment indicator, the method transforms what would normally be a source of image degradation into a useful signal that guides the alignment process, ultimately eliminating the root cause while maintaining the beneficial spherical aberration correction.
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 facilitates axial alignment by focusing on specific aberrations, reducing the burden on operators and decreasing alignment time, while ensuring that aberrations other than the targeted ones do not appear, thus improving spatial resolution.
Implementation Method 1
at least three stages of multipole elements arranged along an optical axis... at least three astigmatic fields are produced by at least three stages of multipole elements
Implementation Method 2
Parts of the orbit of the charged particle beam are moved simultaneously along a direction perpendicular to the optical axis by deflectors mounted between said multipole elements
Data Source
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AI summary
A method of making axial alignment of a charged particle beam (20) relative to at least three stages of multipole elements (11, 12, 13) is offered. Also, a charged particle beam system capable of making the axial alignment is offered. At least three astigmatic fields are produced. Some parts of the orbit of the beam or the distributions of the astigmatic fields, or both, are simultaneously translated in a direction perpendicular to the optical axis (OP) such that astigmatisms of the same order and same type due to axial deviations between successive ones of the astigmatic fields cancel out each other.