Wavelength-Selective Filter Selection for Optical Measurement
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Solution Overview
Problem
Conventional position measurement apparatuses face challenges in accurately reducing light intensity across a wide wavelength band, leading to decreased throughput and increased complexity and cost due to the non-uniform dimming rates of neutral density filters for visible, blue, and infrared light.
Innovation Solution
A measurement apparatus with a first filter unit for selecting different wavelength bands and a second filter unit for reducing light intensity, featuring an obtaining unit to determine the transmittance of each filter and a selection unit to choose the appropriate filters for optimal light control, allowing for precise light adjustment across a wide wavelength band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single neutral density filter is used for all wavelength bands, then the device complexity is reduced, but the light intensity control accuracy deteriorates because the filter cannot implement the same dimming rate for blue and infrared light as for visible light
Solution Approach 1:
The patent applies local quality by providing different neutral density filters for different wavelength bands. Each filter is optimized for its specific wavelength range, ensuring accurate dimming rates for blue, visible, and infrared light separately. This is achieved by having multiple illumination optical systems, each with its own neutral density filter positioned on the optical path, allowing each filter to have wavelength-specific characteristics tailored to its band.
Solution Approach 2:
The patent segments the illumination system into multiple wavelength-specific illumination optical systems (blue, visible, infrared). Each segmented system has its own dedicated neutral density filter, allowing independent optimization of light intensity control for each wavelength band without affecting the others. This segmentation enables precise control while maintaining manageable device complexity through modular architecture.
2Measurement precision
If multiple illumination optical systems are provided for each wavelength band, then the light intensity control accuracy is improved, but the device complexity, size, and cost increase
Solution Approach 1:
The patent applies universality by designing the multiple illumination optical systems to share common structural elements and control mechanisms. The illumination systems use similar optical component arrangements and are controlled by a unified control unit that manages all wavelength bands. This multi-functional design allows the system to achieve wavelength-specific light intensity control while avoiding the need for completely separate systems for each band, thereby reducing overall complexity.
3Manufacturing precision
If the wavelength band of detection light is widened, then the overlay accuracy is improved, but the throughput decreases because time is required to adjust the light amount using neutral density filters with non-uniform dimming rates
Solution Approach 1:
The patent applies preliminary action by pre-configuring the appropriate neutral density filter for each wavelength band before measurement begins. The system includes pre-stored transmittance data for each filter across different wavelength bands, allowing the control unit to quickly select and switch to the correct filter without requiring time-consuming adjustments during operation. This preliminary preparation of filter options and transmittance information enables rapid switching between wavelength bands while maintaining accurate light intensity control.
Solution Approach 2:
The patent implements feedback by having the control unit store and reference the actual transmittance characteristics of each neutral density filter for each wavelength band. The system uses this feedback information to intelligently select the most appropriate filter based on the required wavelength band and desired light intensity, optimizing both measurement accuracy and throughput by avoiding unnecessary filter changes and adjustments.
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 solution enables accurate light control and maintains throughput by selecting the appropriate neutral density filters based on actual transmittance data for each wavelength band, simplifying the optical system and reducing costs.
Implementation Method 1
a first filter unit including a plurality of first filters arranged on an optical path between a light source configured to output light for illuminating the mark and an image sensor configured to capture the mark, each of the plurality of first filters being configured to allow light having a different wavelength band to pass
Implementation Method 2
a second filter unit including a plurality of second filters arranged on the optical path between the light source and the image sensor, and each configured to reduce light intensity of light and allow the light to pass
Data Source
AI summary
The present invention provides a measurement apparatus including a first filter unit including a plurality of first filters, and each configured to allow light having a different wavelength band to pass, a second filter unit including a plurality of second filters, and each configured to reduce light intensity of light and allow the light to pass, an obtaining unit configured to obtain data representing a transmittance of each of the plurality of second filters for a wavelength band of light having passed through each of the plurality of first filters, and a selection unit configured to select, based on the data obtained by the obtaining unit, from the plurality of second filters, one second filter arranged on an optical path together with one first filter among the plurality of first filters.