Charged Particle Beam Convergence Measurement From Defocus Imaging
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Solution Overview
Problem
Charged particle beam systems, such as scanning electron microscopes, face challenges in accurately determining the beam convergence and numerical aperture of focused beams, leading to limitations in resolution due to beam aberrations and deviations from design specifications.
Innovation Solution
A method involving the taking of images at various defocus distances, retrieval of beam cross sections, determination of beam widths, and calculation of beam convergence values, including numerical aperture, to accurately assess beam convergence and aberrations, using a charged particle beam system with a processor and memory to execute these steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the system is designed for a specific numerical aperture to provide excellent operation, then the system performance is optimized, but the actual numerical aperture may deviate from the expected value due to beam aberrations and manufacturing tolerances
Solution Approach 1:
The patent replaces direct mechanical measurement of beam convergence with an optical imaging method. By capturing images of a sample at multiple defocus distances and analyzing the beam cross-section in the images, the numerical aperture is determined optically rather than through direct mechanical measurement, which is prone to errors and deviations from design specifications.
Solution Approach 2:
The patent creates a visual copy of the beam cross-section by imaging the sample at different defocus distances. Instead of measuring the beam directly, the method captures images that represent the beam's spatial distribution, allowing indirect measurement of beam convergence and numerical aperture through image analysis rather than direct beam measurement.
2Manufacturing precision
If beam aberrations are present in the charged particle beam, then the resolution is limited, but the actual cross-sectional shape of the focused beam may differ from the design shape
Solution Approach 1:
The patent intentionally captures images at multiple defocus distances (excessive action) rather than just at the focal plane. By capturing images both in-focus and out-of-focus, the method obtains sufficient data to analyze beam convergence even when the beam cross-sectional shape deviates from design specifications due to manufacturing tolerances or aberrations.
Solution Approach 2:
The patent replaces direct measurement of beam cross-sectional shape with image-based analysis. By substituting direct beam measurement with optical imaging and computational analysis of beam cross-sections in images, the method can accurately determine numerical aperture even when the physical beam shape deviates from design specifications.
3Measurement precision
If one wants to accurately determine the numerical aperture to improve resolution, then more precise measurement methods are needed, but conventional methods lack the precision to account for beam aberrations
Solution Approach 1:
The patent makes the imaging system multi-functional by using it for both sample imaging and beam convergence measurement. The same imaging device that captures sample images is also used to capture beam cross-section information by imaging the sample at different defocus distances, eliminating the need for separate measurement equipment and reducing overall system complexity.
Solution Approach 2:
The imaging system performs self-characterization by using itself to measure its own beam convergence properties. The system captures images that reveal information about its own beam cross-section and numerical aperture, allowing the system to self-diagnose and self-optimize without requiring external measurement equipment.
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 approach allows for reliable determination of beam convergence and numerical aperture, enabling improved resolution and identification of aberrations, thus optimizing the performance of charged particle beam systems.
Implementation Method 1
a focused charged particle beam may be different from the design shape. The resolution limit of a charged particle beam system is determined by the numerical aperture (NA) of the charged particle beam that is focused by an objective lens on a surface of the sample
Implementation Method 2
the primary electron beam generates signal particles like secondary electrons (SE) and/or backscattered electrons (BSE) that can be used to image and/or inspect a sample
Data Source
AI summary
A method of determining a beam convergence of a charged particle beam (11) focused by a focusing lens (120) toward a sample (10) in a charged particle beam system (100) is provided. The method includes (a) taking one or more images of the sample when the sample is arranged at one or more defocus distances from a respective beam focus of the charged particle beam; (b) retrieving one or more beam cross sections from the one or more images; (c) determining one or more beam widths from the one or more beam cross sections; and (d) calculating at least one beam convergence value based on the one or more beam widths and the one or more defocus distances. Further, a charged particle beam system for imaging and/or inspecting a sample that is configured for any of the methods described herein is provided.