Micro Lens Array for Charged Particle Beam Aberration Control
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Solution Overview
Problem
Charged particle beam systems face limitations in throughput and aberration control, particularly in multi-beamlet inspection systems, due to coulomb blur and off-axial aberrations, which restrict the maximum incident angle and overall system performance.
Innovation Solution
A micro lens array structure with a current limiting aperture array and a lens array aligned to minimize aberrations, where the current limiting aperture is positioned symmetrically along the optical axis, and the lens array comprises multiple electrodes to focus beamlets into a flat image plane, reducing field curvature and astigmatism, and optimizing the electric field to enhance beam homogeneity and throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a lens array is used to generate multiple focused beamlets with different incident angles, then throughput is improved, but off-axial aberrations (coma and astigmatism) increase
Solution Approach 1:
The patent divides the single beam system into multiple beamlets using a lens array, where each lens focuses a portion of the diverging beam at a different angle. This segmentation allows parallel processing of multiple beamlets, increasing throughput while managing aberrations through controlled distribution of beam paths across the lens array
Solution Approach 2:
The patent applies different optical characteristics to different regions of the lens array, with each lens element optimized for its specific incident angle range. The lens array is designed with varying focal lengths and aperture sizes across different zones to locally compensate for off-axial aberrations while maintaining overall system throughput
2Productivity
If the maximum incident angle is increased to improve throughput, then beam coverage is improved, but astigmatism becomes dominant and restricts further angle increase
Solution Approach 1:
The patent employs asymmetric lens designs within the lens array, where lenses at different positions have different focal lengths, aperture diameters, and curvature radii. This asymmetric configuration allows each lens to be optimized for its specific incident angle, enabling broader beam coverage while controlling astigmatism through localized optimization rather than uniform design
Solution Approach 2:
The patent systematically varies key optical parameters (focal length, aperture diameter, curvature radius) across the lens array to optimize performance at different incident angles. By changing these parameters progressively from central to peripheral lenses, the system achieves extended angular coverage while maintaining acceptable astigmatism levels through parameter optimization
3Manufacturing precision
If a current limiting aperture is positioned to minimize aberrations, then beam focus quality is improved, but the system complexity increases
Solution Approach 1:
The patent combines the current limiting aperture function with the lens array structure, integrating the aperture plate as part of the lens assembly rather than as a separate component. This merging reduces system complexity by eliminating additional alignment requirements and mechanical structures while maintaining the aberration-minimizing aperture positioning
Solution Approach 2:
The aperture plate serves multiple functions simultaneously: it limits beam current, defines the virtual aperture position for aberration control, and structurally supports the lens array. This multi-functionality reduces the need for separate components and simplifies the overall system design while achieving the desired beam focus quality
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
The solution significantly reduces aberrations and increases the opening angle of beamlets, improving the throughput and uniformity of charged particle beam systems by minimizing geometrical aberrations and maintaining a flat image plane, thereby enhancing the overall performance of the systems.
Implementation Method 1
a lens array comprising a plurality of lenses to focus the beamlets with different incident angles into a plane
Implementation Method 2
a current limiting aperture array located either before or after the lens array, to split up the diverging charged particle beam into a plurality of charged particle beamlets
Data Source
AI summary
The invention relates to a multiple beam charged particle optical system, comprising an electrostatic lens structure with at least one electrode, provided with apertures, wherein the effective size of a lens field effected by said electrode at a said aperture is made ultimately small. The system may comprise a diverging charged particle beam part, in which the lens structure is included. The physical dimension of the lens is made ultimately small, in particular smaller than one mm, more in particular less than a few tens of microns. In further elaboration, a lens is combined with a current limiting aperture, aligned such relative to a lens of said structure, that a virtual aperture effected by said current limiting aperture in said lens is situated in an optimum position with respect to minimizing aberrations total.