Surface Position Detection Using Right-Angled Prism Geometry
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Solution Overview
Problem
Conventional surface position detecting apparatuses experience relative positional deviations between polarization components due to total reflections in rhomboid prisms, leading to unclear pattern images and detection errors, especially when used with photosensitive substrates coated with resist layers, which vary in thickness.
Innovation Solution
The apparatus sets the refractive index of the total reflection prism members and the angle of incidence to satisfy a specific relation, minimizing the relative positional deviation between polarization components by using total reflection surfaces in the optical path, ensuring accurate detection of surface positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If rhomboid prisms with parallel internal reflection surfaces are used to increase the angle of incidence for higher detection accuracy, then the detection accuracy of surface position is improved, but relative positional deviation between polarization components occurs causing unclear pattern images
Solution Approach 1:
The patent changes the physical parameters of the optical system by replacing rhomboid prisms with right-angled prisms and adjusting the angle of incidence to 45 degrees. This parameter change eliminates the relative positional deviation between polarization components while maintaining sufficient detection accuracy for surface position measurement.
Solution Approach 2:
The patent transitions from symmetric rhomboid prisms with parallel reflection surfaces to asymmetric right-angled prisms with perpendicular reflection surfaces. This asymmetric design fundamentally changes the optical path behavior, preventing the polarization component separation that causes image degradation while still enabling accurate surface position detection.
2Measurement precision
If the angle of incidence is increased close to 90 degrees to enhance detection accuracy, then measurement precision is improved, but device complexity increases due to requiring special rhomboid prism configurations
Solution Approach 1:
The patent simplifies the optical system by changing the prism configuration parameter from rhomboid to right-angled prisms and setting the angle of incidence to a standard 45 degrees. This eliminates the need for complex parallel surface alignment while maintaining adequate detection precision through the modified optical geometry.
3Productivity
If total reflection is used in rhomboid prisms to achieve the required beam direction, then optical path efficiency is improved, but Goos-Haenchen shift occurs causing detection errors especially with resist-coated substrates
Solution Approach 1:
The patent modifies the optical parameters by using right-angled prisms with 45-degree incidence angles instead of rhomboid prisms. This changes the total reflection geometry to eliminate the Goos-Haenchen shift effect, thereby removing detection errors caused by resist layer thickness variations while preserving optical path efficiency.
Solution Approach 2:
The patent converts the potential harm of total reflection (which causes Goos-Haenchen shift and detection errors) into a benefit by redesigning the prism geometry. The right-angled prism configuration with 45-degree incidence transforms the reflection behavior to eliminate polarization-related errors, turning a problematic effect into a reliable detection method.
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 enables clear pattern formation and precise surface position detection on photosensitive substrates, even with varying resist layer thickness, by eliminating the Goos-Haenchen Shift and maintaining high detection accuracy.
Implementation Method 1
a total reflection prism member having an internal reflection surface which totally reflects an incident beam
Implementation Method 2
there appears a relative positional deviation between polarization components in the beam totally reflected on the two mutually parallel internal reflection surfaces
Data Source
AI summary
A surface position detecting apparatus includes a light projection system that projects a beam from an oblique direction onto a detection target surface, and a light reception system that receives a beam reflected on the detection target surface, said surface position detecting apparatus adapted to detect a surface position of the detection target surface based on an output from the light reception system. At least one of the light projection system and the light reception system includes a total reflection prism member including an internal reflection surface which totally reflects an incident beam. Upon detection of the surface position of the detection target surface, a refractive index of an optical material forming the total reflection prism member and an angle of incidence of the incident beam to the internal reflection surface of the total reflection prism member are set so as to satisfy a predetermined relation.