Correlating Optical and SEM Images for Wafer Defect Verification
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Solution Overview
Problem
Assessing the sensitivity of an optical inspection system for patterned wafers is a manual and slow process, relying on human operators to correlate defect locations from electronic beam inspectors or scanning electron microscopes, which is inefficient and prone to inaccuracies.
Innovation Solution
A method and system that correlate optical images with scanning electron microscopy images by acquiring and matching the resolution of both types of images using features-of-interest and reference structures, allowing for automatic defect location verification and sensitivity assessment, thereby enhancing the accuracy and speed of defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual defect location correlation is performed by human operators, then defect locations can be verified, but the process is slow and inefficient
Solution Approach 1:
The system performs automatic defect location correlation by having the optical inspection system itself verify its detected defects against SEM images through automated image processing and coordinate transformation, eliminating the need for manual operator intervention while maintaining accurate defect location verification
Solution Approach 2:
The manual mechanical process of operators visually correlating defect locations is replaced with an automated computational system that uses image processing algorithms, coordinate system transformations, and automatic image matching to correlate defect locations between optical and SEM images
2Reliability
If manual defect correlation is performed, then defect sensitivity can be assessed, but the process is prone to human errors
Solution Approach 1:
The system automatically performs defect sensitivity assessment by correlating optical images with SEM images through programmed algorithms, eliminating human error while maintaining reliable defect detection through systematic automated verification processes
Solution Approach 2:
The system uses feedback from the correlation process to automatically assess optical inspection sensitivity, comparing detected defect locations with ground truth from SEM images and using this feedback to validate and refine detection accuracy without manual intervention
3Reliability
If SEM burn marks are created to verify optical images, then sensitivity can be confirmed, but the process is time-consuming and not always possible
Solution Approach 1:
The system performs sensitivity verification in advance by correlating optical images with pre-acquired SEM images before any physical verification steps, using the coordinate transformation and image matching capabilities to confirm sensitivity without requiring time-consuming SEM burn mark creation
Solution Approach 2:
The system creates a virtual copy of the verification process by using digital image correlation and coordinate transformation to replicate the sensitivity verification that would otherwise require physical SEM burn marks, eliminating the need for actual physical modification of the wafer
Data Source
AI summary
The correlation of optical images with SEM images includes acquiring a full optical image of a sample by scanning the sample with an optical inspection sub-system, storing the full optical image, identifying a location of a feature-of-interest present in the full optical image with an additional sources, acquiring an SEM image of a portion of the sample that includes the feature at the identified location with a SEM tool, acquiring an optical image portion at the location identified by the additional source, the image portions including a reference structure, correlating the image portion and the SEM image based on the presence of the feature-of-interest and the reference structure in both the image portions and the SEM image, and transferring a location of the feature-of-interest in the SEM image into the coordinate system of the image portion of the full optical image to form a corrected optical image.