Dynamic Defect Threshold Adjustment for Semiconductor Mask Inspection
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Solution Overview
Problem
Current pattern inspection methods for semiconductor masks struggle with accurately detecting defects in ultra-fine patterns due to increased sensitivity and the need for high manufacturing yield, leading to inefficiencies in defect detection and storage requirements.
Innovation Solution
An inspection method and apparatus that irradiate a sample with lighting light, obtain optical images, and perform comparisons using adjustable defect determination thresholds to identify defects, calculate the number of defects, and adjust thresholds based on defect totals to optimize detection sensitivity and reduce false positives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a fixed defect determination threshold is used for pattern inspection, then the inspection process is simple and fast, but the number of false defect detections increases and storage requirements increase
Solution Approach 1:
The patent applies dynamics by changing the defect determination threshold from a fixed value to a dynamic value that varies based on the inspection location. The threshold is adjusted according to the cumulative number of defects detected so far, allowing the inspection system to adapt its sensitivity throughout the scanning process. This resolves the contradiction by enabling both fast inspection (through automated dynamic adjustment) and accurate defect identification (through location-adaptive thresholds).
Solution Approach 2:
The patent implements parameter changes by modifying the defect determination threshold parameter throughout the inspection process. Instead of using a constant threshold, the system changes the threshold value based on the cumulative defect count and inspection progress. This allows the system to maintain high detection accuracy for critical defects while reducing false positives, thereby improving both measurement precision and productivity.
2Measurement precision
If a low defect determination threshold is used to detect all potential defects, then detection sensitivity increases, but the number of false positives and storage requirements increase
Solution Approach 1:
The patent applies local quality by implementing location-dependent defect determination thresholds. Different regions of the mask receive different threshold values based on their inspection history and cumulative defect counts. Critical areas maintain low thresholds for high sensitivity, while areas with many detected defects use higher thresholds to filter false positives. This resolves the contradiction by enabling high detection sensitivity where needed while reducing the total number of detected defects through localized threshold adjustment.
3Quantity of substance
If a high defect determination threshold is used to reduce false positives, then the number of detected defects decreases, but critical defects may be missed
Solution Approach 1:
The patent implements preliminary action by performing cumulative defect counting and threshold adjustment during the inspection process itself. As defects are detected, the system immediately updates the cumulative count and adjusts subsequent thresholds accordingly. This preliminary tracking and dynamic adjustment ensures that critical defects are not missed (maintaining reliability) while false positives are reduced through adaptive thresholding based on prior detections.
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 effectively reduces the number of excessively detected defects, decreases inspection time, and minimizes storage requirements by dynamically adjusting defect detection thresholds, ensuring accurate identification of critical defects while preventing the detection of nuisance defects.
Implementation Method 1
obtaining a first optical image in which the lighting light transmitted through the first portion is imaged or a second optical image in which the lighting light reflected by the first optical image is imaged
Data Source
AI summary
An inspection method includes: irradiating a first portion of a sample to be inspected with a lighting light; obtaining a first optical image in which the lighting light transmitted through the first portion is imaged or a second optical image in which the lighting light reflected by the first optical image is imaged; based on a first defect determination threshold, performing a first comparison between a first reference image referred to the first optical image and the first optical image or a second comparison between a second reference image referred to the second optical image and the second optical image; determining whether the first portion includes a first defect; storing a first coordinate of the first defect, the first defect determination threshold, the first optical image or the second optical image, and the first reference image or the second reference image in a case where the first portion is determined to have the first defect; calculating the number of first defects in the first portion as a defect total number; calculating a second defect determination threshold increased by a predetermined amount from the first defect determination threshold in a case where the defect total number is larger than the defect number threshold; and equalizing the second defect determination threshold with the first defect determination threshold in a case where the defect total number is equal to or less than the defect number threshold.