Chromatic Aberration Corrector With Segmented Multipole Element
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Solution Overview
Problem
Chromatic aberration in electron microscopes, such as TEM and SEM, deteriorates resolution due to the length of multipole elements, which increases perturbations of the electron beam and affects the ultimate resolution, necessitating efficient production of negative chromatic aberrations to improve resolution.
Innovation Solution
A chromatic aberration corrector with a first multipole element having three portions with superimposed electric and magnetic quadrupole fields, where the electric quadrupole field is stronger in the first and third portions and magnetic in the second, producing two-fold astigmatism components that are opposite in sign, allowing for efficient chromatic aberration correction and reducing the length of the multipole element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the length (thickness) of multipole element is increased, then the chromatic aberration correction capability is improved, but the electron beam undergoes more perturbations from field charging and voltage instability, deteriorating the resolution
Solution Approach 1:
The first multipole element is divided into three portions (first, second, and third portions) along the optical axis, each producing quadrupole fields with different electric-to-magnetic field strength ratios. This segmentation allows the element to generate negative chromatic aberration more efficiently over a shorter total length, reducing the electron beam's exposure to destabilizing fields while maintaining correction capability.
Solution Approach 2:
Different portions of the multipole element have different field configurations: the first and third portions have stronger electric quadrupole fields, while the second portion has a stronger magnetic quadrupole field. This local variation in field quality enables efficient chromatic aberration correction with reduced element length, minimizing perturbations to the electron beam.
2Reliability
If the length (thickness) of multipole element is reduced, then the resolution is improved by reducing perturbations, but the chromatic aberration correction efficiency decreases
Solution Approach 1:
By dividing the multipole element into three functional portions with different field strength ratios, the design achieves efficient negative chromatic aberration generation in a compact form. The segmented structure allows each portion to contribute differently to the overall correction, maximizing correction efficiency within a reduced total length.
Solution Approach 2:
The invention changes the parameters of the electromagnetic fields by varying the ratio of electric to magnetic quadrupole field strength across different portions. This parameter variation enables the element to produce negative chromatic aberration more efficiently, achieving effective correction with a shorter element length that minimizes electron beam perturbations.
3Device complexity
If a single multipole element is used, then the device complexity is reduced, but the chromatic aberration correction efficiency is insufficient
Solution Approach 1:
The single multipole element is segmented into three portions with different field configurations, creating a more efficient correction system without adding separate multipole elements. This internal segmentation allows the element to produce negative chromatic aberration more effectively, improving correction efficiency while maintaining relative structural simplicity.
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 configuration effectively cancels out two-fold chromatic aberration, improving the resolution of the electron microscope by reducing the thickness of the multipole element and minimizing the impact of field charging and voltage instability, thus enhancing the microscope's imaging capabilities.
Implementation Method 1
a first multipole element having a first thickness along an optical axis of an electron beam and producing a first static electromagnetic field
Implementation Method 2
Each of the first, second, and third portions produces a quadrupole field in which an electric quadrupole field and a magnetic quadrupole field are superimposed
Implementation Method 3
Each of the first, second, and third portions produces a quadrupole field in which an electric quadrupole field and a magnetic quadrupole field are superimposed
Implementation Method 4
a second multipole element having a second thickness along the optical axis and producing a second electromagnetic field
Implementation Method 5
The second portion produces a two-fold astigmatism component that is opposite in sign to two-fold astigmatism components produced by the first and third portions
Data Source
AI summary
The chromatic aberration corrector (100) has a first multipole element (110) for producing a first electromagnetic field and a second multipole element (120) for producing a second electromagnetic field. The first multipole element (110) first, second, and third portions (110a, 110b, 110c) arranged along an optical axis (OA) having a thickness and producing a quadrupole field in which an electric quadrupole field and a magnetic quadrupole field are superimposed. In the first and third portions (110a, 110c), the electric quadrupole field is set stronger than the magnetic quadrupole field. In the second portion (110b), the magnetic quadrupole field is set stronger than the electric quadrupole field. The second portion (110b) produces a two-fold astigmatism component that is opposite in sign to two-fold astigmatism components produced by the first portion (110a) and third portion (110c).