Wafer Inspection NA Segmentation and Polarization
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Solution Overview
Problem
Current wafer inspection systems face challenges in achieving optimal signal-to-noise ratio for small particles due to fixed segmentation of the numerical aperture (NA), inefficiencies in polarization management, and compatibility issues with multi-spot illumination, leading to suboptimal performance for various defect types.
Innovation Solution
A system that segments the full collection NA into different segments using an optical element like an apertured mirror, which directs scattered light to separate detectors, and employs a polarizing element to separate polarization components, optimizing each segment for maximum signal-to-noise ratio and minimizing surface scattering noise while maximizing defect detection sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the collection NA is segmented into multiple fixed portions with separate detectors, then the signal-to-noise ratio for specific defect types is improved, but the device complexity increases
Solution Approach 1:
The collection NA is divided into multiple segments (e.g., first NA portion and second NA portion) that are directed to different detectors. This segmentation allows each detector to be optimized for specific defect types, improving the signal-to-noise ratio by reducing surface scattering noise while maintaining the ability to detect various defect characteristics
Solution Approach 2:
The system employs a single mirror collector that can collect light across the full collection NA, making it multi-functional for detecting different defect types. By combining this universal collector with polarization management and NA segmentation, the system achieves specialized detection capabilities without requiring multiple separate collection optics for each defect type
2Measurement precision
If multiple lens collectors are used to divide the collection NA, then detection sensitivity for different defect types is improved, but the optical design complexity and compatibility with multi-spot illumination deteriorate
Solution Approach 1:
The patent replaces multiple lens collectors with a single mirror collector that uses polarization management and NA segmentation achieved through beam splitters and detectors. This substitution simplifies the optical design by eliminating the need for multiple complex lens assemblies while maintaining the ability to divide and detect different NA portions for various defect types
Solution Approach 2:
Instead of using multiple lens collectors to physically divide the collection NA, the system segments the NA portion collected by a single mirror using polarization optics and beam splitters. This approach achieves the same detection sensitivity improvement while reducing optical design complexity and improving compatibility with multi-spot illumination
3Measurement precision
If polarizers are used to suppress surface scattering, then the signal-to-noise ratio is improved, but the optical complexity and phase shift management issues arise
Solution Approach 1:
The system introduces polarization management as an intermediary mechanism between light collection and defect detection. By using polarizers and beam splitters to separate polarization components, the system suppresses surface scattering noise while directing different NA portions to appropriate detectors, achieving high signal-to-noise ratio without requiring complex optical redesign
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 significantly improves the signal-to-noise ratio and sensitivity for defect detection, allowing for more efficient collection and detection of scattered light from particles over a larger area, reducing surface scattering noise, and maintaining simplicity in optics design.
Implementation Method 1
a polarizing element positioned in the path of the scattered light separated into one of the different segments... configured to separate the scattered light in one of the different segments into different portions of the scattered light based on polarization
Implementation Method 2
an optical element configured to separate the scattered light collected in different segments of the collection NA... one portion that reflects the scattered light collected in one segment of the collection NA and another portion that transmits the scattered light collected in another segment
Data Source
Figure 1a
Figure 1b
Figure 1c
AI summary
A system configured to inspect a wafer and its operating method, the system comprising: an illumination subsystem configured to illuminate the wafer; a collection subsystem configured to collect light scattered from the wafer and to preserve the polarization of the scattered light; an optical element configured to separate the scattered light collected in different segments of the collection numerical aperture of the collection subsystem, wherein the optical element is positioned at a Fourier plane or a conjugate of the Fourier plane of the collection subsystem; a polarizing element configured to separate the scattered light in one of the different segments into different portions of the scattered light based on polarization; and a detector configured to detect one of the different portions of the scattered light and to generate output responsive to the detected light, wherein the output is used to detect defects on the wafer.