Wafer Defect Detection Using CAD Data Registration
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Solution Overview
Problem
Current defect localization in very large scale integrated circuits is limited by the low accuracy of inspection tools, which hampers the effectiveness of defect analysis due to coarse registration methods, necessitating more precise methods for die-to-die or cell-to-cell comparison.
Innovation Solution
The method involves generating and registering images of wafer areas relative to CAD data, dividing images into blocks, locating registration targets, determining block offsets, and estimating image offsets to achieve precise defect detection and reporting in CAD coordinates, thereby enhancing registration accuracy and defect localization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If die-to-die registration is performed using conventional inspection tools, then defect comparison can be conducted, but registration accuracy is limited to about 1 micron which is insufficient for high-resolution defect analysis
Solution Approach 1:
The patent introduces CAD data as an intermediary reference framework between the inspection tool and the wafer. Instead of directly registering die images to each other with limited accuracy, the system registers images to the CAD data which provides a high-precision coordinate system. This intermediary enables achieving registration accuracy finer than the imaging pixel size without requiring the inspection tool itself to be more complex.
Solution Approach 2:
The patent segments the registration process into multiple stages: first dividing the wafer image into multiple blocks, then locating registration targets within each block, determining block offsets, and finally estimating the overall image offset. This segmentation allows the system to achieve high registration accuracy by accumulating precise measurements from multiple localized points rather than relying on a single coarse measurement.
2Measurement precision
If higher resolution defect analysis is performed, then defect localization accuracy improves, but the usefulness of CAD data is limited due to low accuracy defect localization reporting
Solution Approach 1:
The patent implements feedback by using the detected defect locations in CAD coordinates to verify and refine the registration accuracy. The system compares the registered defect positions against the expected CAD geometry and uses this feedback to adjust and improve subsequent registration measurements, ensuring that defect location information is accurately captured and reported.
Solution Approach 2:
The patent transitions from two-dimensional pixel-based coordinate systems to three-dimensional CAD coordinate systems that incorporate precise geometric information about the wafer structure. By registering images to the CAD data framework, the system gains an additional dimension of precision through the use of known geometric relationships and multi-layer CAD representations, enabling accurate defect localization even when imaging resolution is limited.
3Reliability
If registration accuracy is improved beyond imaging pixel limits, then defect detection sensitivity is fully extracted, but conventional inspection tools cannot achieve this without additional complexity
Solution Approach 1:
The patent uses CAD data as an intermediary that bridges the gap between conventional inspection tool capabilities and the desired high registration accuracy. The inspection tool remains relatively simple, but by registering images to the precise CAD coordinate system, the system achieves enhanced reliability in defect detection without requiring the inspection tool itself to be more complex.
Solution Approach 2:
The patent performs preliminary actions by pre-processing the CAD data and pre-identifying registration targets before the actual defect inspection. The system divides the wafer into blocks, locates registration targets in advance, and determines block offsets in preparation for the final registration. This preliminary action allows the main inspection process to focus on defect detection with the benefit of pre-established accurate registration frameworks.
Data Source
AI summary
Images of areas of a wafer are generated and registered with respect to computer aided design (CAD) data to provide a registered images. Defects in the wafer are then detected by comparing the registered images to one another and defect location information is generated in CAD coordinates.