Dual Range Focus Detection for Precision Metrology
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Solution Overview
Problem
Existing machine vision inspection systems face limitations in achieving an extended range vs. resolution capability for focus and range detection, particularly in precision dimensional metrology, due to inadequate performance of existing auxiliary focus sensors in tracking surface height changes and maintaining robustness over abrupt steps.
Innovation Solution
A dual range focus detection apparatus is introduced, comprising a broad range focus detector and a high resolution focus detector, with a novel dual range focus detector arrangement that includes a collimation lens, an objective lens, and a beam splitting surface, utilizing a Shack-Hartmann configuration for high resolution and a broad range focus detector sub-aperture along the optical axis for reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single focus sensor is used, then the device complexity is reduced, but the range vs. resolution capability is inadequate
Solution Approach 1:
The focus detection system is segmented into two independent detectors: a first focus detector for high resolution measurements and a second focus detector for broad range measurements. Each detector operates independently within its optimized range, resolving the contradiction by dividing the single detection function into specialized segments that collectively provide both high resolution and extended range capability.
2Measurement precision
If a Shack-Hartmann configuration is used for high resolution, then the measurement precision is improved, but the robustness over abrupt steps deteriorates
Solution Approach 1:
Different detection qualities are assigned to different detectors based on local measurement needs. The first focus detector (Shack-Hartmann) provides high local measurement precision for gradual surface variations, while the second focus detector provides robust broad-range tracking for abrupt steps. The system selectively activates each detector based on the local surface characteristics being measured.
3Adaptability or versatility
If a broad range focus detector is used, then the detection range is extended, but the measurement precision is reduced
Solution Approach 1:
The detection range is segmented into two operational zones: a broad range zone handled by the second focus detector and a high precision zone handled by the first focus detector. The system automatically selects or combines signals from appropriate detectors based on the measurement requirements, ensuring both extended range and high precision are achieved in different operating conditions.
4Device complexity
If existing auxiliary focus sensors are used, then the device complexity is minimized, but the reliability for tracking surface height changes deteriorates
Solution Approach 1:
Two different focus detection technologies are merged into a single integrated system with a common illumination source and optical path. The first and second focus detectors are combined to provide complementary capabilities, achieving high reliability for tracking surface height changes while maintaining manageable system complexity through shared components.
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 solution provides enhanced focus detection and range signals with improved robustness and extended range capability, allowing for precise dimensional metrology and effective tracking of surface height changes, addressing the limitations of existing systems.
Implementation Method 1
a collimation lens arranged to input radiation from the illumination source and output an illumination beam having a fixed degree of collimation
Implementation Method 2
an objective lens arranged to input the illumination beam and to focus the illumination beam at a nominal focus plane along an optical axis
Implementation Method 3
a high resolution focus detector configuration according to a Shack-Hartmann configuration which includes at least one sub-aperture lens located proximate to the optical axis and away from the optical axis, and a photodetector that receives light from that lens
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3B
AI summary
An extended range focus sensor is provided. In various embodiments, the focus sensor may include a relay lens assembly to image a plane between an objective lens and the relay lens arrangement to a plane near an entrance pupil of a focus detector arrangement of the focus sensor. In some embodiments, the objective lens pupil is imaged onto the focus detector entrance pupil. In some embodiments, an illumination beam passes through the relay lens arrangement and is magnified on its way to be output by the objective lens, and the reflected focus detection beam passes back through the objective lens and the relay lens arrangement and is reduced prior to being input to the focus detector arrangement. In some embodiments, the focus detector arrangement may comprising a broad range focus detector combined with a high resolution Shack-Hartmann focus detector, and in others a single extended range Shack-Hartmann focus detector is used.