Charged Particle Beam Convergence via Defocus Profile Matching
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Solution Overview
Problem
Accurately determining the beam convergence of a charged particle beam focused by a focusing lens in charged particle beam systems, particularly to determine the numerical aperture, is challenging due to beam aberrations and the non-linear relationship between beam width and defocus distance.
Innovation Solution
A method involving taking images of a sample at various defocus distances, retrieving beam profiles, simulating beam profiles based on an estimated beam convergence value, and iteratively adjusting this value to minimize the difference between simulated and retrieved profiles, thereby determining the actual beam convergence value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If beam aberrations are present in the charged particle beam system, then the resolution is limited, but the actual beam convergence may still deviate from the expected value making accurate determination difficult
Solution Approach 1:
The patent employs an iterative feedback mechanism where the measured beam width at a specific defocus distance is compared against simulated beam widths calculated from a transfer function. The transfer function parameters are continuously adjusted based on this feedback until the simulated beam width matches the measured beam width, thereby accurately determining the actual beam convergence despite the presence of beam aberrations
Solution Approach 2:
The patent introduces a transfer function as an intermediary mathematical model that relates the defocus distance to the beam width. This transfer function acts as a mediator between the measurable quantity (beam width at defocus) and the desired parameter (actual beam convergence), enabling accurate determination even when direct measurement is compromised by aberrations
2Measurement precision
If the actual numerical aperture deviates from the expected value, then the resolution limit cannot be optimized, but traditional methods cannot accurately determine the actual numerical aperture
Solution Approach 1:
The patent replaces direct mechanical/optical measurement methods with a computational approach. Instead of using complex optical setups to directly measure beam convergence, the system uses image processing and mathematical simulation (transfer function) to calculate the actual numerical aperture from readily obtainable beam width measurements at defocus distances
Solution Approach 2:
The transfer function serves as a mathematical intermediary that connects the easily measurable beam width at defocus to the difficult-to-measure actual beam convergence. By measuring the beam width at a known defocus distance and using the transfer function relationship, the system can indirectly and accurately determine the numerical aperture without direct measurement
3Measurement precision
If one uses a large numerical aperture to improve resolution limit, then the resolution can be improved theoretically, but beam aberrations become more significant and affect actual performance
Solution Approach 1:
The patent uses feedback to measure the actual beam convergence and detect deviations caused by aberrations. By continuously comparing measured beam widths with simulated values and adjusting the transfer function parameters, the system can identify and account for aberration effects, enabling accurate determination of the actual numerical aperture even when aberrations are significant
Solution Approach 2:
The patent converts the harmful effect of beam aberrations into useful information. By measuring how the actual beam width deviates from the ideal beam width at defocus, the system can detect and quantify the presence of aberrations. This deviation information is then used to adjust the transfer function and accurately determine the actual beam convergence, turning the aberration-induced error into a diagnostic tool
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 method allows for the reliable and accurate determination of the beam convergence, specifically the numerical aperture, independent of defocus distance choices, which is essential for improving resolution and identifying beam aberrations.
Implementation Method 1
a focusing lens for focusing the charged particle beam toward a sample placed on the sample stage
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), comprising: (a) taking one or more images (h1 . . . N) of the sample when the sample is arranged at one or more defocus distances (z1 . . . N) from a respective beam focus of the charged particle beam, and retrieving one or more retrieved beam profiles (g1 . . . N) from the one or more images (h1 . . . N); (b) simulating one or more beam profiles at the one or more defocus distances (z1 . . . N) based at least on an estimated beam convergence value (initialC) of the charged particle beam to provide one or more simulated beam profiles (g′1 . . . N); (c) determining a magnitude (R) of a difference between the one or more simulated beam profiles (g′1 . . . N) and the one or more retrieved beam profiles (g1 . . . N); and (d) varying the estimated beam convergence value in an iterative process for reducing or minimizing said magnitude (R) to determine an actual beam convergence value (actualC). Furthermore, a charged particle beam system for imaging and/or inspecting a sample that is configured for any of the methods described herein is provided.