Birefringent Displacement Sensing for Tilt-Tolerant Height Measurement
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Solution Overview
Problem
Existing displacement detection apparatuses face limitations in measuring displacement in the height direction of semiconductor wafers or photomasks due to limited orientation change tolerance and trade-offs between measurement resolution and distance, leading to reduced versatility and accuracy.
Innovation Solution
A displacement detection apparatus utilizing a series of birefringent units to split and superimpose light beams, allowing for high-resolution displacement measurement in the height direction while maintaining a long optical path and accommodating target tilt, by configuring birefringent units to vary phase differences based on target movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If interference-based displacement detection is used, then measurement precision is improved, but adaptability deteriorates due to limited orientation change tolerance
Solution Approach 1:
The patent divides the optical path into multiple segments using a plurality of birefringent units. Each birefringent unit processes the light beam independently, allowing the system to maintain high measurement precision while accommodating orientation changes. The segmented approach enables the detection unit to receive light beams even when the measurement surface is tilted, thus resolving the contradiction between precision and adaptability.
Solution Approach 2:
The patent introduces a new dimension to the optical path by using birefringent units that manipulate the polarization state of light. This dimensional change in the optical path allows the system to maintain interference-based measurement precision while being tolerant to orientation changes, as the birefringent units can compensate for angular deviations.
2Adaptability or versatility
If birefringent prism distance is increased to avoid exposure equipment, then adaptability is improved, but measurement precision deteriorates
Solution Approach 1:
The patent segments the optical path into multiple sections with intermediate birefringent units. This segmentation allows the detection unit to be positioned at a greater distance from the measurement surface while maintaining measurement precision through the cumulative phase modulation effect of multiple birefringent units.
Solution Approach 2:
The birefringent units serve multiple functions: they modulate the phase of light beams, compensate for orientation changes, and enable the system to operate at various distances. This multi-functionality allows the system to achieve both adaptability (long distance) and measurement precision simultaneously.
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
Enables high-precision displacement measurement in the height direction with enhanced versatility, allowing for accurate detection even with target tilt and maintaining a long optical path between the birefringent prism and detection unit.
Implementation Method 1
a first birefringent unit that is provided in an optical path from the light source to the target to which the light is emitted, and splits the light into a first light beam and a second light beam having a phase difference with respect to the first light beam
Implementation Method 2
a second birefringent unit that is provided in optical paths of the first light beam and the second light beam each reflected from the target and refracts the first light beam and the second light beam
Implementation Method 3
a third birefringent unit that is provided in optical paths of the first light beam and the second light beam that have passed through the second birefringent unit, and converges the first light beam and the second light beam
Implementation Method 4
a fourth birefringent unit that is provided in optical paths of the first light beam and the second light beam that have passed through the third birefringent unit, and superimposes the first light beam and the second light beam
Data Source
AI summary
[Problem] To provide a displacement detection apparatus that offers high measurement accuracy while maintaining high versatility.[Solution] A second birefringent unit 121 and a third birefringent unit 123 are configured to change the phase difference between the first light beam L1 and the second light beam L2 in response to movement of the target T in the measurement direction.