Polarization Mirroring for Optical Inspection Signal-to-Noise
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Solution Overview
Problem
Existing optical inspection systems struggle to effectively suppress radiation scattered from sample surfaces while preserving radiation from defects, leading to suboptimal signal-to-noise ratios due to fixed polarization patterns that do not adapt to varying sample surface patterns.
Innovation Solution
The implementation of a polarization mirroring device and a tunable polarization module that transpose and filter scattered radiation based on polarization patterns, allowing for increased flexibility in suppressing surface radiation and enhancing defect detection sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fixed polarizers are used to suppress scattered radiation, then the signal-to-noise ratio is improved for specific sample types, but the system cannot adapt to different sample surface patterns
Solution Approach 1:
The patent applies dynamics by making the polarization state tunable and adjustable rather than fixed. The polarization module can dynamically change its polarization state to match the optimal polarization for different sample types and scattering angles, allowing the system to adapt to varying sample surface patterns while maintaining high signal-to-noise ratio for each specific sample type
Solution Approach 2:
The patent implements parameter changes by varying the polarization state parameter according to the sample type and scattering angle. The system changes the polarization parameters (orientation, ellipticity) to optimize the suppression of surface scattered radiation for different samples, thereby achieving both high measurement precision and adaptability across different sample types
2Object-generated harmful factors
If polarization filtering is applied to suppress surface radiation, then noise is reduced, but defect radiation is also suppressed
Solution Approach 1:
The patent applies local quality by using different polarization filtering strategies for different spatial regions and scattering angles. The system tailors the polarization state to each specific scattering angle and region, applying stronger filtering where surface radiation dominates while preserving signals from defects, thereby reducing noise without excessively suppressing defect radiation
Solution Approach 2:
The system uses feedback by analyzing the polarization patterns of scattered radiation and adjusting the polarization filtering accordingly. The feedback mechanism allows the system to distinguish between surface radiation patterns and defect radiation patterns, dynamically adjusting the filtering to suppress surface noise while preserving defect signals
3Measurement precision
If segmentation of collection numerical aperture is used with different polarizers, then fixed polarization patterns are accounted for, but the system lacks flexibility when polarization patterns change
Solution Approach 1:
The patent implements universality by creating a single polarization module that can perform multiple functions - it can operate at different polarization states to handle various scattering angles and sample types. This universal module replaces the need for multiple fixed polarizers and collectors, reducing device complexity while maintaining the ability to account for different polarization patterns through software-controlled parameter adjustment
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 improves the signal-to-noise ratio by removing mirror symmetry in polarization patterns, enabling more effective suppression of surface radiation and enhanced defect sensitivity across different samples.
Implementation Method 1
a polarization mirroring device arranged to transpose a polarization state of a portion of the radiation that has been scattered from a surface of a sample
Implementation Method 2
a polarization module that filters the collected radiation based on polarization
Data Source
AI summary
Systems and methods for optical inspection of a sample are provided. Radiation scattered from the sample includes a first portion having a first polarization state and a second portion having a second polarization state that is a mirror image of the first polarization state. The first polarization state of the first portion of the scattered radiation is transposed using a polarizing mirroring device so that the scattered radiation output from the polarizing mirroring device has substantially the second polarization state.