Electron-Beam Wafer Inspection for Stable Contour Extraction
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Solution Overview
Problem
Existing electron-beam defect inspection apparatuses face challenges in accurately extracting contour lines of miniaturized patterns due to decreased edge intensity and edge-to-edge distances smaller than the size of edge filters, leading to instability and reduced noise resistance and positional precision.
Innovation Solution
An inspection apparatus and method that captures SEM images to enhance signal-to-signal differences at material edge segments, using a first threshold to generate a line based on a predetermined function in a matrix of pixels, and compares a reference image with an inspection image to improve contour line extraction accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the edge filter size is decreased to extract contour lines of miniaturized patterns, then the extraction capability for small edge-to-edge distances is improved, but the noise resistance and positional precision deteriorate
Solution Approach 1:
The patent divides the image processing into multiple stages: first extracting candidate contour pixels using one-dimensional spatial filters in horizontal and vertical directions, then determining final contour pixels through additional filtering and connectivity analysis. This segmentation allows the use of small filter sizes for edge detection while maintaining precision through multi-stage verification
Solution Approach 2:
The patent applies different filtering strategies to different pixel types: candidate contour pixels are identified using directional filters, then subjected to additional local connectivity checks and noise filtering. This localized quality control maintains positional precision while enabling extraction of fine contour details
2Manufacturing precision
If the edge filter size is decreased to extract contour lines of miniaturized patterns, then the extraction capability for small edge-to-edge distances is improved, but the noise resistance deteriorates
Solution Approach 1:
The patent segments the noise filtering process into multiple stages: initial candidate selection using directional filters, followed by connectivity-based filtering, and final verification through comparison with adjacent pixels. This multi-stage approach maintains noise resistance while enabling extraction of fine contour details
Solution Approach 2:
The patent implements feedback mechanisms where extracted contour candidates are verified against local image characteristics and connectivity requirements. Pixels that fail verification are rejected, providing feedback-based noise suppression that maintains reliability without sacrificing extraction capability
3Productivity
If conventional contour extraction methods are used with miniaturized patterns, then the processing speed is maintained, but the extraction accuracy deteriorates due to gentle edge profiles
Solution Approach 1:
The patent performs preliminary action by first identifying candidate contour pixels using simple directional filters before applying more complex connectivity and verification tests. This preliminary filtering reduces the number of pixels requiring intensive processing, maintaining speed while improving accuracy
Solution Approach 2:
The patent employs dynamic processing where the filtering stringency and processing depth are adjusted based on local image characteristics. Regions with clear edges undergo simpler processing while regions with gentle profiles receive more intensive multi-stage filtering, optimizing the balance between speed and accuracy
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
Enhances the accuracy of contour line extraction in electron-beam defect inspection, particularly for miniaturized patterns, by stabilizing the extraction process and maintaining noise resistance and positional precision.
Implementation Method 1
to obtain a large signal-to-signal difference (referred to as a 'rich material contrast' hereinafter) at segments at which secondary electrons are emitted with varying intensities according to the type of the material of the irradiation surface, namely, edge segments of the pattern by irradiating a sample with an electron beam
Data Source
AI summary
According to an embodiment, an inspection apparatus includes an image capturing mechanism configured to capture a first image of a wafer or a mask, a first circuit configured to calculate a first threshold based on a plurality of gradation values of the first image, a second circuit configured to generate a first line based on a predetermined function using the first threshold in a second pixel provided in a matrix of n×m first pixels with n rows and m columns included in the first image, where n and m are integers of two or greater, a third circuit configured to calculate a first point in the second pixel by using the first line, and a comparison circuit configured to compare a reference image with an inspection image that is based on the first point.