Off-Axis Electron Micro-Lens for Tunable Coma Correction
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Solution Overview
Problem
Charged particle systems, such as electron microscopes, face challenges in correcting spherical aberration and coma due to the inherent positive spherical aberration coefficient of electromagnetic lenses, leading to imaging errors and increased costs for additional correctors.
Innovation Solution
An electron optical module is introduced, comprising a structure downstream of the electron source, an electron lens assembly, and a micro-lens off the optical axis, which applies aberrations to create a tunable coma by combining the effects of the lens assembly and micro-lens to achieve desired aberration values in downstream planes, including compensation for spherical aberration, coma, field curvature, and astigmatism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electromagnetic lenses are used to focus electron beams, then focusing capability is achieved, but spherical aberration and coma are introduced
Solution Approach 1:
The patent introduces a micro-lens that intentionally adds spherical aberration to the electron beam. This harmful aberration from the micro-lens is designed to counterbalance and cancel the spherical aberration produced by the main electromagnetic objective lens, thereby converting a harmful factor into a beneficial correction mechanism
Solution Approach 2:
The micro-lens is deliberately positioned off the optical axis of the electron beam, creating an asymmetric configuration. This asymmetric placement is essential for generating the specific type and amount of spherical aberration needed to cancel the aberration from the main lens, while introducing only minimal additional coma
2Measurement precision
If additional correctors are added to correct spherical aberration and coma, then imaging accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent combines the aberration correction function with the existing electron optical system by integrating a simple micro-lens into the electron beam path. This merges the correction capability into the existing focusing system rather than adding separate, complex corrector devices
Solution Approach 2:
The patent achieves aberration correction by adjusting parameters of existing components - specifically the position, size, and voltage of the micro-lens - rather than adding new complex devices. By changing these parameters, the desired aberration cancellation is achieved with minimal additional complexity
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 solution allows for the tuning of aberrations in the off-axial electron beam, effectively reducing or eliminating coma and other aberrations, thereby improving the resolution and magnification of charged particle systems while reducing the need for costly correctors.
Implementation Method 1
a micro-lens that is not positioned on the optical axis of the electron lens assembly and that applies a lensing effect to an off-axial election beam
Implementation Method 2
the electromagnetic lenses used to focus the electron beams in electron microscopes always have a positive spherical aberration coefficient
Data Source
AI summary
An electron optical module for providing an off-axial electron beam with a tunable coma, according to the present disclosure includes a structure positioned downstream of an electron source and an electron lens assembly positioned between the structure and the electron source. The structure generates a decelerating electric field, and is positioned to prevent the passage of electrons along the optical axis of the electron lens assembly. The electron optical module further includes a micro-lens that is not positioned on the optical axis of the electron lens assembly and is configured to apply a lensing effect to an off-axial election beam. Aberrations applied to the off-axial electron beam by the micro-lens and the electron lens assembly combine so that a coma of the off-axial beam has a desired value in a downstream plane.