Wafer Inspection Displacement Analysis Using CAD Correlation
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Solution Overview
Problem
Current wafer inspection systems face challenges in accurately determining displacement and detecting defects across multiple scanned frames and areas, particularly due to variations in scanning directions and inconsistencies between design data and scanned images.
Innovation Solution
A system and method that utilize a displacement analysis module to calculate and process displacements for multiple targets within scanned frames, generating calibration information and a target database in CAD coordinates, and a defect detection module to identify defects using run-time displacements and modified comparison schemes, enabling accurate defect detection across different wafer areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple scanned frames are used to cover the entire wafer area, then the inspection coverage is improved, but the displacement accuracy deteriorates due to scanning direction variations and frame-to-frame inconsistencies
Solution Approach 1:
The wafer inspection area is divided into multiple scanned frames that are processed separately. Each frame undergoes independent displacement analysis by correlating its image data with corresponding design data, allowing local displacement variations to be captured without compromising overall coverage
Solution Approach 2:
Design data serves as an intermediary reference between multiple scanned frames. By correlating each scanned frame's image data with the authoritative design data, the system establishes a common reference framework that enables accurate displacement determination across all frames despite scanning direction variations
2Measurement precision
If correlation-based displacement calculation is used for each target, then the displacement determination accuracy is improved, but the processing time increases
Solution Approach 1:
The processing is segmented into two phases: an offline calibration phase where displacement analysis is performed in detail to generate calibration information, and an online inspection phase where pre-computed calibration data is applied. This segmentation allows accurate correlation-based calculations to be performed only when necessary, reducing overall processing time
Solution Approach 2:
Calibration information including displacement data is pre-computed and stored during an offline phase. This preliminary action allows the system to avoid performing time-consuming correlation calculations during actual inspection, as the displacement characteristics are already determined and stored for rapid application
3Productivity
If alternating scanning directions are used to cover different wafer areas, then the inspection efficiency is improved, but the defect detection accuracy deteriorates due to direction-dependent displacement variations
Solution Approach 1:
The system applies direction-specific displacement analysis by separately processing frames scanned in different directions. Calibration information is generated and applied according to the specific scanning direction of each frame, allowing the system to account for direction-dependent displacement variations while maintaining high inspection efficiency through alternating scan patterns
Data Source
AI summary
A system for generating calibration information usable for wafer inspection, the system including: (I) a displacement analysis module, configured to: (a) calculate a displacement for each target out of multiple targets selected in multiple scanned frames which are included in a scanned area of the wafer, the calculating based on a correlation of: (i) an image associated with the respective target which was obtained during a scanning of the wafer, and (ii) design data corresponding to the image; and (b) determining a displacement for each of the multiple scanned frames, the determining based on the displacements calculated for multiple targets in the respective scanned frame; and (II) a subsequent processing module, configured to generate calibration information including the displacements determined for the multiple scanned frames, and a target database that includes target image and location information of each target of a group of database targets.