Wien Filter Imaging for High Probe Currents
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Solution Overview
Problem
Current charged particle beam apparatuses are limited by small apertures, restricting high probe currents needed for applications like EDX and WDX analysis and electron beam inspection, due to chromatic aberration and spherical aberration limitations.
Innovation Solution
An imaging apparatus with a Wien filter and a 2*m-pole element, where the first lens is upstream of the Wien filter's entrance opening and the second lens is downstream of its exit opening, allowing for dispersion-free imaging and enabling high beam currents by balancing dispersion within the Wien filter, thus accommodating high probe current modes without the constraints of prior corrector designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If small apertures or diaphragms are used to limit the aperture angle in a Wien filter monochromator, then chromatic aberration is reduced, but the maximum beam current is limited
Solution Approach 1:
The patent divides the beam path into two separate imaging systems: an upstream imaging system that forms an intermediate image at the Wien filter entrance, and a downstream imaging system that forms the final image. This segmentation allows the Wien filter to operate without aperture limitations while maintaining chromatic aberration correction through the monochromator function.
Solution Approach 2:
The patent introduces an intermediate image plane as a mediator between the object and final image. The upstream imaging system creates this intermediate image at the Wien filter entrance, which then serves as the object for the downstream imaging system. This intermediary approach decouples the aperture angle limitation from the beam current constraint.
2Measurement precision
If the Wien filter is used for monochromation, then energy width is reduced, but the apparatus cannot operate in high probe current mode
Solution Approach 1:
The patent makes the Wien filter serve dual functions: as a monochromator for chromatic aberration correction and as a dispersion-free imaging element for high probe current mode. By configuring the upstream and downstream imaging systems to both form stigmatic images, the Wien filter can operate in either mode depending on the excitation of the multipole element, providing universal functionality.
Solution Approach 2:
The patent makes the imaging properties of the Wien filter dynamic by adjusting the excitation of the multipole element. When the multipole element is excited, the system operates in high probe current mode with dispersion-free imaging. When the multipole element is not excited or differently excited, the system operates in monochromator mode with chromatic aberration correction.
3Measurement precision
If conventional corrector designs are used, then chromatic and spherical aberrations are corrected, but the apparatus is constrained by small aperture requirements
Solution Approach 1:
The patent moves the image formation process to a different dimensional configuration by using two separate imaging systems (upstream and downstream) rather than a single corrector system. The upstream system forms an intermediate image in object space, and the downstream system forms the final image, effectively adding a dimensional separation that eliminates aperture constraints.
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 allows for virtually rotational symmetric, dispersion-free Gaussian imaging, enabling higher beam currents and flexible operation between high probe current and monochromator modes, enhancing the capabilities of charged particle beam devices for applications requiring increased throughput and resolution.
Implementation Method 1
Wien filters are known as monochromators for charged particles wherein an electrostatic dipole field and a magnetic dipole field are superimposed perpendicularly to each other
Implementation Method 2
The imaging apparatus according to the invention comprises a first lens, a Wien filter with an entrance opening and an exit opening and a second lens, wherein the Wien filter further comprises a 2*m-pole element, m≧2
Implementation Method 3
a first lens, wherein said first lens is disposed upstream of said first opening of the Wien filter... an intermediate image plane of the first lens is located between said first opening and said first lens
Implementation Method 4
a second lens, wherein said second lens is disposed downstream of said second opening of the Wien filter... an intermediate object plane of the second lens is located between said second opening and said second lens
Data Source
AI summary
An imaging apparatus is provided, comprising a first lens, a Wien filter having a first opening and a second opening, and further comprising a 2*m-pole element, m≧2, and a second lens, wherein said first lens is disposed upstream said first opening of the Wien filter and said second lens is disposed downstream said second opening of the Wien filter, and an intermediate image plane of the first lens is located between said first opening and said first lens and an intermediate object plane of the second lens is located between said second opening and said second lens, and wherein said Wien filter is adapted for dispersion-free imaging of a stigmatic image formed in said intermediate image plane of said first lens into a stigmatic image formed in said intermediate object plane of said second lens.