SEM Defect Inspection Focusing Method
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Solution Overview
Problem
Existing defect inspection methods using electron microscopes require extensive time for focusing due to a shallow depth of field and the need for cumbersome focus map registration, especially when Z coordinates corresponding to XY coordinates are not close between substrates.
Innovation Solution
A defect inspection device and method that uses a scanning electron microscope to sequentially image multiple portions of a sample, estimating a curved surface shape by adjusting the focal point in a wide range initially and then narrowing the range for precise focusing, reducing the scanning range and time required for focusing without the need for extensive focus map registration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the Z coordinate is moved in a wide range to perform focusing on substrates with different Z coordinates, then focusing accuracy is improved, but the time required for focusing increases
Solution Approach 1:
The patent applies preliminary action by performing a rough focusing operation in a wide Z coordinate range first to identify the approximate focal region, then performing a refined focusing operation in a narrower range around the estimated focus point. This two-stage approach pre-establishes the search space boundaries before the final focusing measurement, reducing the total time while maintaining accuracy.
Solution Approach 2:
The patent segments the focusing process into two distinct stages: a first focusing operation that scans a wide Z coordinate range to locate the approximate focal region, and a second focusing operation that scans a narrower Z coordinate range around the estimated focus point. This segmentation allows the system to efficiently narrow down the search space without sacrificing final focusing precision.
2Measurement precision
If a focus map is registered by measuring Z coordinates for many XY coordinates, then focusing accuracy across the substrate is improved, but the complexity of the inspection process increases
Solution Approach 1:
The patent extracts only the essential information needed for focusing by performing rough focusing at a limited number of representative XY coordinate positions to estimate the curved surface shape, rather than measuring Z coordinates across the entire substrate. This extraction approach obtains sufficient focusing information while eliminating the cumbersome task of comprehensive focus map registration.
Solution Approach 2:
The patent creates a simplified model of the substrate surface by estimating the curved surface shape from limited rough focusing measurements, then uses this copied surface model to guide the refined focusing operation. This copying approach allows the system to generalize from a few measurement points to the entire substrate area without requiring exhaustive measurements.
3Loss of time
If the scanning range of the Z coordinate is reduced for faster focusing, then focusing time is reduced, but focusing accuracy deteriorates when Z coordinates differ significantly between substrates
Solution Approach 1:
The patent performs a preliminary rough focusing operation in a wide Z coordinate range first to estimate the substrate's curved surface shape and identify the approximate focal region. This preliminary action establishes informed boundaries for the subsequent refined focusing operation, allowing the second stage to use a narrower scanning range without sacrificing accuracy, thus reducing total focusing time while maintaining precision.
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 significantly reduces the time needed for focusing on various substrates and eliminates the cumbersome task of registering focus maps, allowing for efficient defect inspection across different substrates with improved accuracy.
Implementation Method 1
a scanning electron microscope that irradiates a sample with a focused electron beam, performs scanning, and thereby acquires an SEM image of the sample
Implementation Method 2
to perform the scanning by moving a focal point of the electron beam in a normal direction relative to a surface of the sample in a predetermined range; to adjust the focal point of the electron beam to the surface of the sample
Data Source
AI summary
In imaging a sample using an electron microscope, in order to reduce a time for focusing, a scanning range of a Z coordinate is reduced to complete focusing by obtaining SEM images such that: for a first predetermined number of portions, focal positions of an electron beam in obtaining each SEM image are moved in a predetermined range; then, a curved surface shape of the surface of the sample is estimated by using information relating to the focal positions of the electron beam in the first predetermined number of portions; after the images are taken, the range in which the focal positions of the electron beam are moved for scanning the electron beam on the surface of the sample is made to be narrower than the predetermined range by using the curved surface information estimated, thereby performing scanning to take the images of the sample.