Coupling Mirror Geometry for Brightfield-Darkfield Separation
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Solution Overview
Problem
Existing optical inspection systems face challenges in efficiently separating and directing brightfield and darkfield light signals for effective defect detection on substrates, particularly due to inaccuracies in the positioning and geometry of light separators, which affect the size and shape of the transmissive region.
Innovation Solution
The design of a coupling mirror with a minimized transmissive region is optimized by determining the overlap volume between the illumination light and the separator, accounting for errors and non-ideal components, and enlarging this volume to accommodate tolerances, ensuring maximum passage of illumination light and effective separation of light signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the transmissive region of the light separator is minimized to fit the illumination light, then the separation efficiency of brightfield and darkfield signals is improved, but the system becomes highly sensitive to positioning and geometry errors
Solution Approach 1:
The patent performs preliminary geometric modeling and intersection volume calculation during the design phase to determine the optimal transmissive region shape and size. By pre-calculating the exact geometry needed to accommodate illumination light while maintaining separation efficiency, the system achieves reliable signal separation without requiring ultra-high manufacturing precision during assembly
Solution Approach 2:
The patent transforms the transmissive region from a simple geometric shape to a complex shape defined by the intersection volume of multiple illuminated rays. This parameter transformation allows the region to adapt to the specific illumination geometry, maximizing separation efficiency while being tolerant to manufacturing variations
2Manufacturing precision
If the transmissive region is enlarged to accommodate tolerances, then the positioning sensitivity is reduced, but the amount of darkfield light reaching the detector decreases
Solution Approach 1:
The patent extends the transmissive region from a two-dimensional aperture to a three-dimensional intersection volume that accounts for ray angles and depths. This dimensional expansion allows the region to accommodate positioning tolerances in multiple dimensions while maintaining precise control over which light rays pass through, thereby preserving darkfield light quantity
Solution Approach 2:
The patent divides the transmissive region into multiple segments corresponding to different illumination rays and angles. By segmenting the region according to the geometric intersection of individual rays, the system can selectively transmit appropriate light paths while blocking others, maintaining darkfield light quantity even with enlarged tolerance accommodation
3Productivity
If the transmissive region shape is precisely defined by geometric intersection, then the illumination light passage is maximized, but the device complexity increases
Solution Approach 1:
The patent creates a geometric model (copy) of the illumination light paths and calculates their intersection volume to define the transmissive region. This modeling approach allows precise determination of the optimal region shape without requiring complex physical prototypes or iterative adjustments, thereby maximizing light transmission while managing design complexity through computational methods
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 efficiency of light signal separation, allowing for improved detection of defects by maximizing the amount of dark field light directed towards the detector, thereby improving the inspection process.
Implementation Method 1
said reflective surface is arranged to reflect a peripheral portion of said light beam transmitted from said objective lens arrangement corresponding to the darkfield channel
Implementation Method 2
said transmissive region is arranged to allow therethrough a central portion of said light beam transmitted from said objective lens arrangement corresponding to the brightfield channel
Data Source
AI summary
A wafer inspection tool comprising an illumination system having: a field of view (FOV); a light source pupil having a size and shape; a central optical axis; and one or more field angle defining a shape of said FOV extending away from said light source pupil; an objective lens arrangement including an objective and a plurality of interchangeable telescopes coupled thereto, the objective lens arrangement being configured to collect light reflected off a plurality of field points on the wafer and to onwardly transmit a light beam formed from the collected light; and a light separator having a first reflective surface with a transmissive region formed therein and a second surface, wherein said transmissive region is arranged to allow therethrough a central portion of said light beam transmitted from said objective lens arrangement corresponding to the brightfield channel while said reflective surface is arranged to reflect a peripheral portion of said light beam transmitted from said objective lens arrangement corresponding to the darkfield channel; a relay module configured to relay said light source pupil to said transmissive region; wherein said transmissive region has a shape defined as a geometric intersection volume between a model of said illumination light and said reflective surface and said second surface; wherein said model includes a plurality of solids each solid having a cross section of said light source pupil and angled to a field angle of said one or more field angle.