Scan Waveform Correction for Deflection Coil Distortion
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Solution Overview
Problem
Existing scanning electron microscopes face challenges in correcting various types of image distortions beyond magnification distortion, leading to reduced observation throughput, increased memory requirements, and decreased accuracy in image stitching due to the need for extensive Look Up Tables (LUTs and repeated measurements.
Innovation Solution
A charged particle beam device with a deflection coil, D/A converter, and scan waveform generation unit that uses a basic LUT and linear or curve approximation correction circuits to correct distortions in real-time, reducing memory requirements and maintaining throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If correction values for all conditions are stored in advance in LUT, then distortion correction accuracy is improved, but memory capacity requirements increase enormously
Solution Approach 1:
The patent divides the correction process into two segments: a basic LUT storing only deflection coil distortion correction values (reducing memory size), and a correction value generation unit that calculates condition-specific corrections (magnification, scanning speed, raster rotation) in real-time. This segmentation allows accurate multi-condition correction without requiring enormous memory capacity for pre-storing all correction values.
Solution Approach 2:
The patent transitions from a static LUT approach (storing all correction values in advance) to a dynamic approach where correction values are generated in real-time based on current observation conditions. The correction value generation unit dynamically calculates appropriate correction values using the basic LUT as reference and adjusting for current magnification, scanning speed, and raster rotation settings.
2Measurement precision
If LUT contents are rewritten for each condition, then distortion correction accuracy is improved, but memory writing time increases
Solution Approach 1:
The patent performs preliminary action by pre-storing only the fundamental deflection coil distortion correction values in the basic LUT during device setup. This preliminary correction data serves as a foundation that can be rapidly adjusted for different observation conditions without requiring time-consuming rewriting of the entire LUT for each condition change.
Solution Approach 2:
The patent replaces the mechanical LUT rewriting process with a computational approach. Instead of physically rewriting memory contents for each condition change, the system uses the correction value generation unit to computationally derive appropriate correction values from the basic LUT and current observation parameters, significantly reducing the time required to adapt to different conditions.
3Measurement precision
If central portion of waveform is used for imaging, then distortion correction is improved, but scanning time increases and observation throughput decreases
Solution Approach 1:
The patent implements feedback by using the basic LUT (derived from measured distortion characteristics) to continuously guide real-time correction value generation across the entire scanning waveform. This allows accurate distortion correction to be applied throughout the full scanning range without needing to restrict imaging to the central, less distorted portions of the waveform, thereby maintaining high observation throughput.
Solution Approach 2:
The patent changes the approach from spatial restriction (using only central waveform portions) to parameter-based correction (applying condition-specific correction values across the entire waveform). By dynamically adjusting correction parameters based on current magnification, scanning speed, and raster rotation settings, the system achieves accurate distortion correction throughout the full scanning area without sacrificing scanning speed or throughput.
4Measurement precision
If repeated measurements are performed to correct distortion, then correction accuracy is improved, but observation throughput decreases
Solution Approach 1:
The patent performs the time-consuming distortion measurement action preliminarily during device setup or calibration, storing the results in the basic LUT. This preliminary measurement captures the fundamental deflection coil distortion characteristics that remain relatively constant. Subsequent observations can then use this pre-acquired data with real-time parameter adjustments, eliminating the need for repeated measurements and maintaining high observation throughput.
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 device effectively corrects various distortions without reducing observation throughput, improving image quality, and enhancing the accuracy of image stitching while reducing costs and memory usage.
Implementation Method 1
a deflection coil that scans the charged particle beam on the specimen
Implementation Method 2
a D/A converter that converts a digital scan waveform to an analog scan waveform and outputs the analog scan waveform to the deflection coil
Data Source
AI summary
It is aimed to properly correct the various types of distortion without a reduction in observation throughput. The present disclosure provides a charged particle beam device that obtains an image by irradiating a specimen with a charged particle beam and includes: a deflection coil that scans the charged particle beam on the specimen; a D/A converter that converts a digital scan waveform into an analog scan waveform and outputs the analog scan waveform to the deflection coil to drive the deflection coil; and a scan waveform generation unit that generates a digital scan waveform and outputs the digital scan waveform to the D/A converter, in which the scan waveform generation unit has a basic LUT that stores parameters for correcting the digital scan waveform and includes a correction circuit that corrects a distortion characteristic of the deflection coil.