Segmented Polarizer for Surface Inspection Noise Reduction
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Solution Overview
Problem
Current scanning surface inspection systems face challenges in increasing sensitivity towards small particulates and defects due to noise from surface microroughness, which masks the detection of smaller particles and defects, and existing solutions focus on minimizing this noise rather than optimizing the signal-to-noise ratio for defect detection.
Innovation Solution
A polarizing device is employed that optimizes the signal-to-noise ratio by selectively transmitting scattered radiation from particulates and defects while blocking noise from surface microroughness, using a configuration of polarizing segments with varying polarization axes to maximize the capture rate of defects, even at a less-than-optimal signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical scattering techniques are used to detect particulates on silicon wafers, then the ability to diagnose deviations from ideal conditions is improved, but noise from surface microroughness masks the detection of smaller particles and defects
Solution Approach 1:
The polarizer is divided into multiple segments with different polarization orientations. Each segment is positioned to collect scattered light from a specific angular region, allowing selective transmission of defect signals while blocking microroughness noise through polarization filtering in each segment.
Solution Approach 2:
Different segments of the polarizer have locally optimized polarization properties tailored to their specific angular collection regions. This allows each segment to maximize defect detection sensitivity for its designated angular range while contributing to overall noise reduction when combined with other segments.
2Reliability
If a segmented polarizer is used to optimize signal-to-noise ratio for defect detection, then the capture rate of defects is improved, but the device complexity increases
Solution Approach 1:
The polarizer is divided into multiple segments with different polarization orientations. Each segment is positioned to collect scattered light from a specific angular region, allowing selective transmission of defect signals while blocking microroughness noise through polarization filtering in each segment.
Solution Approach 2:
The segmented polarizer structure serves multiple functions simultaneously: it acts as both a light collection system with specific angular acceptance and a polarization filter. This multi-functionality reduces the need for separate components and simplifies the overall system architecture despite the segmented design.
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 the detection of small particulates and defects by increasing the signal-to-noise ratio, leading to a higher capture rate of defects, despite a potentially lower signal-to-noise ratio, thereby improving the system's sensitivity and accuracy in identifying defects.
Implementation Method 1
The detected light is polarized in a plane that is substantially parallel to the plane of scattering
Implementation Method 2
a small fraction of the beam is 'scattered' into other directions. The amount of light scattered is generally representative of the roughness of the surface and the presence of particulates thereon
Data Source
AI summary
A polarizing device may be used with sample inspection system having one or more collection systems that receive scattered radiation from a region on a sample surface and direct it to a detector. The polarizing device disposed between the collection system(s) and the detector. The polarizing device may include a plurality of polarizing sections. The sections may be characterized by different polarization characteristics. The polarizing device is configured to transmit scattered radiation from defects to the detector and to block noise from background sources that do not share characteristics with scattered radiation from the defects from reaching the detector while maximizing a capture rate for the defects the detector at a less than optimal signal-to-noise ratio.