Adaptive Wafer Image Alignment Using Scored Lock Positions
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Solution Overview
Problem
Current semiconductor inspection tools face challenges in accurately aligning wafer images with reference images due to noise, distortion, and the difficulty in differentiating accurate from inaccurate alignments, especially with small feature sizes and periodic patterns, leading to high nuisance rates and reduced defect detection efficiency.
Innovation Solution
An adaptive alignment method that computes an alignment score for potential lock positions, compares it with stored scores, and updates the database to select the best alignment point, allowing for automatic improvement of alignment accuracy without manual intervention and increasing throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional alignment methods are used to align wafer images with reference images, then alignment can be performed, but alignment accuracy deteriorates due to noise, distortion, and difficulty in differentiating accurate from inaccurate alignments
Solution Approach 1:
The system computes an alignment score for each potential lock position and uses this score as feedback to determine the best alignment point. The alignment score provides quantitative feedback that enables the system to differentiate between accurate and inaccurate alignments, resolving the contradiction by introducing a measurable criterion for alignment quality.
Solution Approach 2:
The system changes the parameter used for alignment evaluation by computing alignment scores based on image matching criteria rather than relying on conventional alignment methods. This parameter change enables more accurate differentiation between correct and incorrect alignments, improving both measurement precision and reliability.
2Measurement precision
If manual intervention is used to select alignment points, then alignment accuracy can be improved, but productivity decreases due to reduced inspection throughput
Solution Approach 1:
The system performs self-service by automatically computing alignment scores and selecting the best lock position without manual intervention. The automated selection process maintains alignment accuracy while eliminating the need for manual review, thereby preserving inspection throughput and resolving the contradiction between precision and productivity.
Solution Approach 2:
The system replaces the mechanical process of manual alignment point selection with an automated computational system that calculates alignment scores. This substitution eliminates manual intervention while maintaining or improving alignment accuracy, thus preserving productivity.
3Measurement precision
If alignment scores are computed and compared for multiple positions, then alignment accuracy improves, but device complexity increases due to additional computing requirements
Solution Approach 1:
The system segments the alignment process by evaluating multiple potential lock positions independently and computing alignment scores for each segment. This segmentation allows the system to identify the best alignment point through comparison while keeping the computational complexity manageable by processing positions in discrete, evaluable units.
Data Source
AI summary
A method for aligning a wafer image with a reference image, comprising: searching for a targeted reference position on the wafer image for aligning the wafer image with the reference image; and in response to a determination that the targeted reference position does not exist: defining a current lock position and an area that encloses the current lock position on the wafer image; computing an alignment score of the current lock position; comparing the alignment score of the current lock position with stored alignment scores of positions previously selected in relation to aligning the wafer image with the reference image; and aligning the wafer image with the reference image based on the comparison.