Multi-Location Autofocus Illumination for Large-Area Focus Stability
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Solution Overview
Problem
High throughput optical inspection systems face challenges in maintaining consistent focus across large sample surfaces with varying thickness, curvature, or surface topography, leading to inaccurate or incomplete inspection results due to complex optical arrangements and sensitivity to alignment and manufacturing variances.
Innovation Solution
An auto-focus system utilizing a simplified optical design with field splitting and decentered slits, incorporating a mask with dual slits and segmented optical elements, and a splitter positioned near the image plane to minimize complexity and enhance transmission intensity while maintaining focus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complex optical arrangements are used to maintain focus across large sample surfaces, then focus consistency may be improved, but device complexity and susceptibility to alignment errors increase
Solution Approach 1:
The patent divides the optical system into distinct functional segments: an illumination path that generates multiple spot arrays across the sample, and a collection path that separately collects and processes light from these spots. This segmentation allows each path to be optimized independently, reducing overall system complexity while maintaining focus consistency across the large sample surface.
Solution Approach 2:
The illumination and collection paths share common optical components and the same imaging area, allowing a single optical system to perform both illumination and collection functions. This multi-functionality reduces the number of separate components needed, thereby reducing device complexity while maintaining reliable focus across the sample surface.
2Measurement precision
If multiple optical components are used to achieve field splitting and focus control, then focus precision may be improved, but sensitivity to alignment and manufacturing variances increases
Solution Approach 1:
The patent uses a simplified mask with only two slits rather than a complex multi-element aperture system. This partial action approach provides sufficient focus precision for the application while significantly reducing the number of components that could introduce alignment errors or manufacturing variances.
Solution Approach 2:
The system creates multiple spot arrays by illuminating the sample at different angles, effectively copying the illumination pattern across the sample surface. This allows focus information to be obtained from multiple locations simultaneously without requiring multiple separate optical paths, thereby maintaining precision while reducing sensitivity to alignment errors.
3Device complexity
If simplified optical design is used, then device complexity is reduced, but transmission intensity and focus quality may deteriorate
Solution Approach 1:
The patent merges the illumination and collection paths into a single integrated optical system that shares common components including the objective lens, mask, and imaging area. This merging allows the system to achieve effective light transmission by utilizing the same optical path for both functions, compensating for the simplified design and maintaining adequate transmission intensity.
Solution Approach 2:
The system continuously illuminates the sample with multiple spot arrays and continuously collects light from these spots through the same optical path. This continuous action ensures that sufficient light intensity is maintained throughout the process, compensating for the reduced number of optical components and maintaining focus quality despite the simplified design.
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 achieves near-diffraction-limited spot arrays with reduced sensitivity to tolerances, improving focus consistency and reducing complexity, cost, and susceptibility to misalignment, while capturing an expanded field of view with minimal optical components.
Implementation Method 1
illuminate a sample with illumination beams that form multiple spot arrays on the sample
Implementation Method 2
focus the collected beams along a first axis while imaging the entrance pupil along a second axis
Data Source
AI summary
An auto-focus system that includes (i) an illumination path that is configured to illuminate a sample with illumination beams that form multiple spot arrays on the sample that comprises an upstream set of spot arrays formed on a first side of an imaging area, and a downstream set of spot arrays formed on another side of the imaging area; (ii) a collection path that comprises an entrance pupil and is configured to collect collected beams that are emitted from the sample, and focus the collected beams along a first axis while imaging the entrance pupil along a second axis to provide optically processed beams. The sensor is configured to generate detection signals that represent the optically processed beams. The controller is configured to determine a focus state of an evaluation beam that impinges on imaging area.