Wafer Defect Detection via Image Smear Equalization
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Solution Overview
Problem
Conventional methods for inspecting microscopic objects like wafers are inadequate in detecting defects due to limitations in comparing images and identifying anomalies, particularly in bright-field and dark-field illuminated scenarios, leading to false alarms and misdetected defects.
Innovation Solution
A method involving image division into sub-images, comparison with defectless references, variance estimation, and further analysis of defect candidates using threshold values and peer-group filtering to accurately identify defects, while accounting for noise and image alignment to minimize false positives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple images are aligned and compared to generate a reference, then defect detection sensitivity is improved, but false alarms increase due to misalignment-induced smear
Solution Approach 1:
The patent applies preliminary action by performing alignment and smear equalization on images before generating the reference. The system pre-processes each image to equalize smear caused by sub-pixel misalignment, then combines them into a reference image. This preliminary processing ensures that when defect detection is performed, the reference image does not contain artificial defects from misalignment, thereby reducing false alarms while maintaining high defect detection sensitivity.
2Measurement precision
If sub-pixel alignment is performed to improve image registration, then measurement precision improves, but device complexity increases due to additional processing steps
Solution Approach 1:
The patent applies parameter changes by modifying the smear parameter of multiple images to be equal before combining them. Instead of performing complex sub-pixel alignment that would significantly increase device complexity, the system changes the smear parameter of each image to match a reference smear level. This approach achieves sufficient image registration accuracy for defect detection while keeping the processing complexity manageable through a simpler parameter equalization process.
Data Source
AI summary
A method for inspecting a wafer including a multiplicity of dies, the method including dividing an image of at least a portion of the wafer into a plurality of sub-images each representing a sub-portion of the wafer and selecting at least one defect candidate within each sub-image by comparing each sub-image to a corresponding sub-image of a reference including a representation, which is assumed to be faultless, of the portion of the wafer.