Aberration Correction Value Calculation Unit for Charged Particle Beam Apparatus
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Solution Overview
Problem
Conventional charged particle beam apparatuses require extensive time for aberration correction due to high noise levels in image data, which slows down the scanning process and increases specimen damage.
Innovation Solution
The apparatus scans a specimen with a primary charged particle beam while changing focus conditions to acquire two-dimensional intensity distribution data, calculates directional derivative values, and uses these to determine aberration parameters for controlling the aberration corrector, thereby reducing noise and speeding up the correction process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high S/N ratio image data is obtained by slowing the scanning speed, then measurement precision of aberration parameters is improved, but productivity is deteriorated due to increased correction time
Solution Approach 1:
The patent extracts only the essential information needed for aberration measurement by calculating asymmetry from directional derivatives of image intensity distribution. This selective extraction of critical features (asymmetry in different directions) allows accurate aberration parameter determination without requiring high S/N ratio images obtained through slow scanning, thus resolving the contradiction between measurement precision and productivity
Solution Approach 2:
The patent performs preliminary calculation of directional derivatives and asymmetry metrics from the acquired images before final aberration parameter determination. By pre-processing the image data to extract asymmetry characteristics in different directions, the method enables rapid aberration measurement without requiring multiple slow scans to achieve high S/N ratio, thereby improving correction speed while maintaining accuracy
2Productivity
If the scanning speed is increased to improve productivity, then aberration correction time is reduced, but measurement precision deteriorates due to noise in the image data
Solution Approach 1:
The patent converts the harmful effect of noise in fast-scanned images into a benefit by using asymmetry calculation from directional derivatives. The asymmetry metric is relatively robust to noise, allowing accurate aberration parameter extraction even from coarse, noisy images obtained at high scanning speeds, thus resolving the contradiction between productivity and measurement precision
3Measurement precision
If conventional Fourier transformation methods are used to obtain aberration parameters, then measurement precision is improved, but loss of time increases due to extensive processing requirements
Solution Approach 1:
The patent replaces the complex mechanical/computational process of Fourier transformation with a simpler mathematical approach based on directional derivatives and asymmetry calculation. This substitution of the image processing method enables rapid aberration parameter determination while maintaining measurement precision, directly addressing the time loss issue
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 rapid aberration correction and reduced specimen damage by accurately obtaining aberration parameters even from coarse images, enabling faster scanning and shorter correction times.
Implementation Method 1
A charged particle beam apparatus (for example, an electron microscope such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM)) necessarily uses a lens that utilizes an electric field or magnetic field in order to focus a charged particle beam
Implementation Method 2
an aberration corrector comprises multipole lenses arranged in multiple stages, and generates an electric field or a magnetic field within the multipole lenses in order to remove aberration included in a charged particle beam
Implementation Method 3
an aberration corrector comprises multipole lenses arranged in multiple stages, and generates an electric field or a magnetic field within the multipole lenses
Implementation Method 4
a charged particle beam apparatus that scans a specimen by irradiation of a charged particle beam to obtain secondary electrons from the specimen
Data Source
AI summary
A charged particle beam apparatus includes: a correction image acquisition part 52 for making a detector 20 acquire items of two-dimensional image data at different focal positions; a directional differentiation operation part 53 for obtaining directional derivative values in a plurality of directions for each of the items of two-dimensional image data at different focal positions; an aberration parameter calculation part 54 for obtaining aberration parameters according to previously determined methods by using the directional derivative values in a plurality of directions for each of the items of two-dimensional image data; an aberration correction value calculation part 55 for obtaining correction values for aberrations by using the aberration parameters; and a control part 56 for setting the correction values in a correction optical system control means to make an aberration corrector 16 correct the aberrations.