Masked Autofocus Optics for Large-Area Focus Consistency
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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 topography due to complex optical arrangements that introduce distortions, reduce transmission intensity, and are susceptible to misalignment.
Innovation Solution
A simplified optical system using a mask with dual slits and field splitting, combined with a splitter and segmented optical elements, maintains optical performance by minimizing complexity and sensitivity to tolerances, enhancing transmission intensity and sensitivity without risking sample damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a complex optical arrangement is used to maintain focus across large sample regions, then focus consistency is improved, but device complexity increases and transmission intensity is reduced
Solution Approach 1:
The optical system is segmented into distinct functional modules: illumination path with independent illumination beams, collection path with separate collection beams, mask with multiple slits, and sensor with multiple detection regions. This segmentation allows each component to be optimized independently while maintaining overall focus consistency across large sample regions, reducing the complexity of the overall optical arrangement.
Solution Approach 2:
A mask positioned between the sample and sensor acts as an intermediary element. The mask with its multiple slits selectively transmits collection beams while blocking others, enabling focus measurement without requiring complex optical arrangements. This intermediary simplifies the optical path while maintaining the ability to measure and maintain focus consistency.
2Reliability
If a complex optical arrangement is used to maintain focus across large sample regions, then focus consistency is improved, but transmission intensity is reduced
Solution Approach 1:
The system extracts only the necessary information for focus measurement by using a mask with selective slits that allow specific collection beams to pass through. This extraction approach avoids the need for complex optical arrangements that would attenuate the light, thereby maintaining high transmission intensity while still achieving focus consistency.
Solution Approach 2:
The system uses partial action by illuminating only specific regions of the sample with illumination beams and collecting only the necessary collection beams through the mask slits. This partial approach reduces the total light path and minimizes energy loss, maintaining high transmission intensity while ensuring focus consistency across the imaged region.
3Device complexity
If a simplified optical system is used, then device complexity is reduced, but measurement precision may be compromised
Solution Approach 1:
The illumination and collection paths are merged in space, with illumination beams and collection beams traveling through the same optical path. This merging allows the use of a simplified optical system while maintaining measurement precision, as the same optical components are used for both illumination and collection, ensuring consistent optical performance.
Solution Approach 2:
The mask serves multiple functions: it acts as an aperture stop, a beam splitter, and a focus measurement element. The sensor also serves dual purposes by detecting both illumination and collection beams. This multi-functionality reduces the need for additional specialized components, maintaining measurement precision while simplifying the overall optical system.
4Ease of manufacture
If a simplified optical system is used, then ease of manufacture is improved, but sensitivity may be reduced
Solution Approach 1:
The system optimizes parameters such as the number, position, and dimensions of the mask slits, as well as the arrangement of illumination and collection beams, to achieve high sensitivity with a simplified optical structure. By carefully adjusting these parameters, the system maintains manufacturing simplicity while ensuring adequate sensitivity for focus measurement.
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 high-level performance with reduced complexity, improved sensitivity, and expanded field of view capture, minimizing alignment issues and cost, while maintaining accurate focus across large sample regions.
Implementation Method 1
a mask that is located at an entrance pupil, the mask comprises a pair of off-axis slits for truncating each collected beam to provide a pair of rays per each collected beam
Implementation Method 2
a beam splitter that is configured to (i) direct to a first branch, first rays associated with the first collected beams, and (ii) direct to an second branch, rays associated with the second collected beams
Implementation Method 3
a sensor that follows the first branch and the second branch and is configured to receive a pair of spots per each one of the multiple spot arrays, wherein a distance between spots of each pair is indicative of a focus state associated with a corresponding spot array
Implementation Method 4
an illumination path that is configured to illuminate a sample with illumination beams that form multiple spot arrays on the sample that comprises a first 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
Data Source
AI summary
A method for auto-focusing by an auto-focus system, the method includes (a) illuminating a sample with illumination beams that form multiple spot arrays on the sample, wherein the spot arrays comprise 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; (b) collecting collected beams emitted from the sample along a collection path that comprises an entrance pupil; (c) focusing the collected beams along a first axis while imaging the entrance pupil along a second axis to provide optically processed beams; (d) generating detection signals that represent the optically processed beams; and (e) determining a focus state of an evaluation beam that impinges on the imaging area.