Spatially-Varying Polarization Rotator for Particle Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current particle detection systems in semiconductor processing face challenges in achieving high sensitivity due to surface scattering noise, which limits measurement sensitivity and degrades image quality, especially on optically polished surfaces.
Innovation Solution
A dark-field imaging system that includes an illumination source, off-axis illumination optics, collection optics, a phase mask, a polarization rotator with spatially-varying polarization rotation, and a polarizer to separate surface haze from particle scattering by rotating and filtering light to specific polarization angles, allowing for improved sensitivity and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If surface scattering suppression methods are applied, then measurement sensitivity is improved, but image quality is degraded
Solution Approach 1:
The collection aperture is segmented into multiple regions (first collection aperture and second collection aperture) with different numerical apertures. The first collection aperture collects scattered light from particles, while the second collection aperture collects surface scattering light. This segmentation allows selective processing of different light components to improve sensitivity without degrading image quality.
Solution Approach 2:
Different polarization rotation angles are applied to different spatial regions of the collected light. A first polarization rotator rotates polarization of light from the first collection aperture by a first angle, while a second polarization rotator rotates polarization of light from the second collection aperture by a second angle. This local quality approach enables selective suppression of surface scattering while preserving particle scattering information.
2Measurement precision
If dark-field imaging is used to detect particles, then sensitivity is improved, but surface scattering noise increases
Solution Approach 1:
The system extracts surface scattering light from the total collected light using a second collection aperture with a larger numerical aperture. The extracted surface scattering light is then rotated by a second polarization rotator and blocked by a polarizer, effectively removing the harmful surface scattering noise while preserving the particle scattering signal.
Solution Approach 2:
A polarizer is introduced as an intermediary component between the polarization rotators and the detector. The polarizer selectively transmits or blocks light based on its polarization state, enabling the system to separate and eliminate surface scattering noise from the particle scattering signal without directly modifying the detection mechanism.
3Object-generated harmful factors
If polarization filtering is applied to reduce surface haze, then signal-to-noise ratio is improved, but detection capability for small particles is reduced
Solution Approach 1:
The system uses adjustable polarization rotators that can dynamically change the polarization rotation angles. This dynamic adjustment allows the system to optimize the balance between surface haze suppression and particle detection capability, adapting to different detection requirements and particle sizes.
Solution Approach 2:
The system adds a polarization dimension to the light collection process. By collecting light through multiple apertures with different numerical apertures and applying different polarization rotations, the system creates additional degrees of freedom for separating surface haze from particle signals, thereby improving detection capability without sacrificing noise reduction.
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
The system effectively enhances sensitivity and image quality by selectively filtering out surface haze, enabling the detection of smaller particles and improving signal-to-noise ratio, thus addressing the limitations of existing technologies.
Implementation Method 1
the polarization rotator includes an optically-active material with an optic axis oriented perpendicular to the second pupil plane that rotates a polarization of light in the second pupil plane based on optical activity
Implementation Method 2
the phase mask is configured to provide different phase shifts for light in two or more pupil regions of a collection area to reshape a point spread function of light scattered from one or more particles
Implementation Method 3
a polarizer aligned to reject light polarized along the selected polarization angle
Implementation Method 4
one or more collection optics to collect scattered light from the sample in response to the illumination beam in a dark-field mode
Data Source
AI summary
A system may include illumination optics to direct an illumination beam to a sample at an off-axis angle, collection optics to collect scattered light from the sample, and a phase mask located at a first pupil plane to provide different phase shifts for light in two or more pupil regions of a collection area to reshape a point spread function of light scattered from one or more particles on a surface of the sample. The system may further include a polarization rotator located at a second pupil plane, where the polarization rotator provides a spatially-varying polarization rotation angle selected to rotate light scattered from the surface of the sample to a selected polarization angle, a polarizer to reject light polarized along the selected polarization angle, and a detector to generate a dark-field image of the sample based on light passed by the polarizer.