Surface Inspection System with Reference Surface Comparison
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Solution Overview
Problem
The existing SP1TBI system faces challenges in detecting anomalies on patterned wafers and surfaces with background noise, as it requires re-scanning and struggles with die-to-die comparison due to rotational motion between the illumination beam and the surface, leading to difficulties in accurately identifying potential anomalies.
Innovation Solution
The system stores radiation intensities from both potential anomaly locations and their surrounding areas, allowing for microview without re-scanning, and enables comparison of corresponding areas on different surfaces by ensuring similar relative locations and orientations, improving defect detection on patterned wafers by segmenting radiation collection and using multiple detectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the SP1TBI system uses threshold-based anomaly detection, then defect sensitivity on unpatterned wafers is improved, but the system produces false anomalies on patterned wafers and surfaces with background noise
Solution Approach 1:
The patent introduces a reference surface as an intermediary to mediate between the illuminated surface and the anomaly detection process. By comparing the illuminated surface to a reference surface that has been illuminated similarly, the system can distinguish true anomalies from background noise and pattern artifacts. The reference surface acts as a mediator that provides contextual information about what constitutes normal variation versus actual defects.
Solution Approach 2:
The patent changes the detection parameter from absolute intensity thresholding to relative intensity comparison. Instead of comparing pixel intensities against a fixed threshold, the system compares intensities between corresponding locations on the illuminated surface and reference surface. This parameter transformation allows the system to adapt to different surface types and illumination conditions, reducing false positives on patterned wafers while maintaining sensitivity to real defects.
2Quantity of substance
If the system stores only pixel intensities above threshold, then data storage efficiency is improved, but the ability to perform microview and compare surrounding areas is worsened
Solution Approach 1:
The patent performs preliminary action by storing the intensity difference map before final anomaly determination. By calculating and storing the differences between illuminated and reference surface intensities for all pixels (not just those above threshold), the system preserves the ability to perform microview and re-examination of surrounding areas. This preliminary storage of differential data enables later analysis without requiring re-scanning, as the comparative information is already captured.
Solution Approach 2:
The patent creates a copy of the intensity difference information in a processed form (difference map) that can be independently analyzed. This copied differential data allows the system to perform microview operations and comparisons without accessing or re-processing the original raw intensity data, thereby enabling efficient post-processing and re-examination of specific regions of interest.
3Speed
If rotational motion is used between illumination beam and surface, then inspection speed is improved, but die-to-die comparison accuracy is worsened due to different illumination angles
Solution Approach 1:
The patent uses the reference surface as an intermediary that captures the effects of rotational motion and varying illumination angles. By comparing both the illuminated surface and reference surface to the same reference, the system compensates for angular variations introduced by rotation. The reference surface serves as a mediator that absorbs the variability caused by different illumination geometries, enabling accurate die-to-die comparison despite rotational motion during inspection.
4Measurement precision
If re-scanning is performed for microview mode, then anomaly verification capability is improved, but inspection time and productivity are worsened
Solution Approach 1:
The patent performs preliminary action by storing the intensity difference map during the initial scan, capturing all comparative information before any anomaly determination is made. This preliminary storage of differential data eliminates the need for re-scanning in microview mode, as all necessary comparative information is already available in the stored difference map. The system can instantly re-examine any region by accessing the pre-computed differential data, maintaining full verification capability without additional inspection time.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances defect detection sensitivity by allowing immediate review of anomaly locations without re-scanning, reduces noise from patterns, and improves comparison accuracy between surfaces with similar patterns, leading to faster and more accurate anomaly identification.
Implementation Method 1
The SP1TBI system determines the presence of potential anomalies by comparing intensities of detector outputs with a threshold. If the intensity of radiation detected by the detector exceeds the threshold, a potential anomaly is then determined to be present at the location from which the scattered radiation is detected.
Data Source
AI summary
Pixel intensities indicative of scattered radiation from portions of the inspected surface surrounding a location of a potential anomaly are also stored so that such data is available for quick review of the pixel intensities within a patch on the surface containing the location of the potential anomaly. Where rotational motion is caused between the illumination beam and the inspected surface, signal-to-noise ratio may be improved by comparing the pixel intensities of pixels at corresponding positions on two different surfaces that are inspected, where corresponding pixels at the same relative locations on the two different surfaces are illuminated and scattered radiation therefrom collected and detected under the same optical conditions.