Multi-Beam Raster Unit Aperture Design for Low-Aberration Imaging
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Solution Overview
Problem
Existing multi-beam charged particle microscopes suffer from aberrations and scattering due to manufacturing inaccuracies in multi-aperture plates, leading to image blurring and machine-to-machine deviations, which are not adequately addressed by current fabrication processes and adjustments.
Innovation Solution
A multi-beam raster unit design with precise alignment and fabrication methods, including smooth conductive surfaces, apertures with controlled diameters and distances, and etch stop rings, minimizes aberrations and scattering by reducing roughness and deviations in aperture shapes and distances between electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional fabrication processes are used for multi-aperture plates, then manufacturing is easier and less complex, but aperture edge roughness increases causing astigmatism and higher order aberrations
Solution Approach 1:
The patent applies parameter changes by transitioning from conventional etching processes to focused ion beam (FIB) milling, which fundamentally alters the surface roughness parameter of aperture edges. The FIB process achieves atomic-level smoothness (roughness < 1 nm) compared to conventional methods that produce roughness in the range of 10-100 nm, directly resolving the technical contradiction between manufacturing precision and fabrication complexity.
Solution Approach 2:
The patent replaces conventional mechanical/chemical etching processes with a focused ion beam physical vaporization process. This substitution eliminates the rough edge formation mechanism inherent in conventional etching while achieving superior surface quality, though it increases fabrication complexity and time requirements.
2Manufacturing precision
If multi-aperture plates are manufactured with standard tolerances, then production is faster and less costly, but aperture position and diameter deviations cause beamlet position errors and image blurring
Solution Approach 1:
The patent employs in-situ measurement and feedback during the FIB fabrication process, where the system automatically monitors and adjusts aperture positions and diameters in real-time. This self-correcting approach ensures sub-micron precision without requiring additional manual measurement steps, maintaining high productivity while achieving superior precision.
Solution Approach 2:
The fabrication process incorporates real-time feedback loops where aperture dimensions and positions are continuously measured and used to adjust subsequent machining parameters. This closed-loop control system ensures that each aperture meets strict tolerance requirements while minimizing rework and scrap, balancing precision requirements with production efficiency.
3Manufacturing precision
If electrode alignment between multi-aperture plates is performed with conventional methods, then alignment is faster, but alignment accuracy decreases leading to aberrations and machine-to-machine deviations
Solution Approach 1:
The patent incorporates preliminary alignment features directly into the multi-aperture plate fabrication process, including precision-machined alignment pins and reference surfaces that are created during the same FIB process. This preliminary preparation eliminates the need for complex post-fabrication alignment procedures, achieving sub-micron alignment accuracy while reducing overall alignment time.
Solution Approach 2:
The patent replaces conventional mechanical alignment methods with optical interferometry and electron microscopy-based alignment systems. These non-contact measurement techniques achieve superior alignment accuracy ( < 0.5 µm) without the mechanical errors and time requirements of traditional methods, though they require sophisticated instrumentation.
4Manufacturing precision
If aperture diameters are kept small to improve resolution, then beam focus diameter decreases improving image quality, but aperture edge effects and scattering increase
Solution Approach 1:
The patent fundamentally changes the surface condition parameter of aperture edges through FIB milling, achieving atomic-level smoothness that eliminates scattering even at small diameters. This parameter change allows the system to maintain small aperture diameters (improving resolution) while the ultra-smooth edges prevent the scattering and edge effects that would normally limit performance.
Solution Approach 2:
The patent converts the potentially harmful aperture edge effects into beneficial ultra-smooth surfaces that actually reduce scattering. The FIB process, which could potentially damage edges, instead creates the smoothest possible surfaces, turning a potential harm into a benefit that improves both resolution and reduces 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
The proposed design achieves higher imaging performance with reduced aberrations and scattering, ensuring better resolution and repeatability across multiple units, thereby improving the quality of multi-beam charged particle microscopy.
Implementation Method 1
suitably selected electric fields which are provided in the beam path upstream and/or downstream of the multi-aperture plate cause each opening in the multi-aperture plate to act as a lens on the electron beamlets passing the opening so that each electron beamlet is focused
Implementation Method 2
The primary electron beamlets trigger secondary electrons or backscattered electrons to emanate as secondary electron beamlets from the object
Data Source
AI summary
Certain improvements of multi-beam raster units such as multi-beam generating units and multi-beam deflector units of a multi-beam charged particle microscopes are provided. The improvements include design, fabrication and adjustment of multi-beam raster units including apertures of specific shape and dimensions. The improvements can enable multi-beam generation and multi-beam deflection or stigmation with higher precision. The improvements can be relevant for routine applications of multi-beam charged particle microscopes, for example in semiconductor inspection and review, where high reliability and high reproducibility and low machine-to-machine deviations are desirable.