Multipole Corrector for Fifth-Order Aberration Correction
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Solution Overview
Problem
Existing correctors for scanning electron microscopes and transmission electron microscopes are limited in their ability to correct higher-order aberrations such as fifth-order spherical aberration and astigmatism, often introducing additional errors like circular errors and coma, and fail to fully compensate for chromatic aberrations.
Innovation Solution
The corrector design incorporates four multipole elements with specific field configurations, including quadrupole and octupole fields, and an additional twelve-pole element between the second and third multipole elements, generating superimposed octupole and twelve-pole fields at astigmatic intermediate images to correct color and spherical aberrations, with magnetic and electric fields used to achieve precise beam correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If four multipole elements with quadrupole and octupole fields are used to correct chromatic and spherical aberrations, then correction capability is improved, but device complexity increases
Solution Approach 1:
The corrector is divided into four separate multipole elements, each responsible for specific field generation (quadrupole or octupole). This segmentation allows independent optimization of each element's function while maintaining overall correction capability, resolving the contradiction between correction capability and structural complexity.
Solution Approach 2:
Each multipole element is designed to generate multiple field types (quadrupole and octupole fields) through configurable current applications. This multi-functionality reduces the need for separate dedicated components for each field type, thereby improving correction capability without proportionally increasing device complexity.
2Manufacturing precision
If additional twelve-pole element is inserted to correct fifth-order spherical aberration, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The twelve-pole element is positioned at a specific location where the beam cross-section is round (between astigmatic intermediate images), creating a region of equipotential symmetry. This strategic positioning allows the element to effectively correct fifth-order spherical aberration without requiring additional elements, as the symmetric position maximizes correction efficiency.
3Measurement precision
If non-rotationally symmetrical fields are used to correct aberrations according to Scherzer theorem, then measurement precision is improved, but object-generated harmful factors increase
Solution Approach 1:
The corrector applies non-rotationally symmetrical fields (quadrupole and octupole) in advance to counteract aberrations before they fully develop in the imaging system. By introducing corrective astigmatism and beam distortions early in the beam path, the system pre-compensates for subsequent aberrations, eliminating the need for larger corrective measures later and reducing overall harmful effects.
Solution Approach 2:
The corrector intentionally introduces controlled astigmatic intermediate images and beam distortions through non-rotationally symmetrical fields. These initially harmful effects are precisely controlled to serve as intermediate steps that enable subsequent correction of chromatic and spherical aberrations, ultimately improving overall image quality.
4Reliability
If antisymmetrical corrector arrangement is used to correct errors, then reliability is improved, but device complexity increases
Solution Approach 1:
The corrector employs an antisymmetrical arrangement of multipole elements around a central plane, where elements are positioned and configured to create opposite beam influences. This asymmetry is deliberately designed to cancel out specific higher-order errors that would be present in symmetrical arrangements, improving correction robustness for fifth-order aberrations.
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 eliminates errors up to the fifth order, reducing residual aberrations and ensuring high-resolution, high-contrast raster images by correcting chromatic and spherical aberrations while minimizing introduction of new errors.
Implementation Method 1
the first and fourth are used to generate quadrupole fields and the second and third to be used to generate octupole fields
Implementation Method 2
the second and third to be used to generate octupole fields and Quadrupole fields are used, the latter being superimposed magnetic and electric fields
Implementation Method 3
by means of astigmatic intermediate images in the second and third multipole elements, color error correction and A spherical aberration correction is possible
Implementation Method 4
an additional twelve-pole element is inserted between the second and third multipole element and is supplied with current and/or voltage in such a way that a An octupole field superimposed with a twelve-pole field is created
Implementation Method 5
an octupole field superimposed with a twelve-pole field is created
Implementation Method 6
Quadrupole fields are used, the latter being superimposed magnetic and electric fields
Implementation Method 7
color error correction and A spherical aberration correction is possible
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The corrector (10) has multipole elements (2, 3) formed as twelve-pole elements using twelve-pole fields for correcting high order error. An additional twelve-pole element (13) is inserted between the multipole elements and loaded with current and/or voltage. An octupole field is super imposed on the twelve-pole fields, where an arrangement of the additional twelve-pole element is effected such that the octupole field and the twelve-pole fields lie at a position between astigmatic intermediate images. A round shaped beam width is provided at the position.