Dark Field Microscope Movable Zeroth Order Block
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Solution Overview
Problem
Dark field microscopes and metrology devices face limitations in the range of acceptance angles for illumination and detection, which restricts the effective Numerical Aperture (NA) in both illumination and detection paths.
Innovation Solution
The implementation of an objective lens arrangement that directs illumination onto a specimen and collects scattered radiation, while a zeroth order block is used to block zeroth order radiation. This setup allows for an illumination scan over multiple subsets of illumination angles and a simultaneous detection scan that adjusts the zeroth order block or scattered radiation to correspond with the illumination, effectively increasing the NA in both paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed zeroth order block is used to block zeroth order radiation, then the dark field measurement can be performed, but the range of acceptance angles for illumination and detection is limited, restricting the effective Numerical Aperture (NA)
Solution Approach 1:
The patent applies the dynamics principle by making the zeroth order block movable instead of fixed. The zeroth order block is positioned to block zeroth order radiation from reaching the detector, and can be moved to different positions to accommodate different illumination angles. This dynamic positioning enables the system to scan through multiple subsets of illumination angles while maintaining effective blocking of zeroth order radiation, thereby increasing the effective Numerical Aperture without compromising the dark field measurement capability.
2Reliability
If the zeroth order block margin is increased to ensure proper blocking, then zeroth order radiation can be effectively blocked, but the necessary block margin reduces the available detection angle range
Solution Approach 1:
The patent resolves this contradiction by implementing a movable zeroth order block that can be dynamically positioned. Instead of requiring a large fixed margin to ensure blocking effectiveness across all angles, the block can be moved to the appropriate position corresponding to each illumination angle. This dynamic adjustment maintains reliable zeroth order blocking while maximizing the available detection angle range, as the block only needs to provide margin for the current illumination angle being measured.
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 effective NA in illumination and detection, allowing for improved resolution and measurement accuracy in dark field metrology, while maintaining flexibility and reducing the necessary zeroth order block margin.
Implementation Method 1
the objective lens arrangement defines a maximum range of illumination angles for accepting the illumination in an illumination path and a maximum range of detection angles for accepting scattered radiation in a detection path; scattered radiation comprising zeroth order radiation and higher order diffracted radiation
Implementation Method 2
a zeroth order block operable to block the zeroth order radiation
Data Source
AI summary
A dark field metrology device includes an objective lens arrangement and a zeroth order block to block zeroth order radiation. The objective lens arrangement directs illumination onto a specimen to be measured and collects scattered radiation from the specimen, the scattered radiation including zeroth order radiation and higher order diffracted radiation. The dark field metrology device is operable to perform an illumination scan to scan illumination over at least two different subsets of the maximum range of illumination angles; and simultaneously perform a detection scan which scans the zeroth order block and/or the scattered radiation with respect to each other over a corresponding subset of the maximum range of detection angles during at least part of the illumination scan.