Dual Pass Interferometer With Segmented Mirror For Unlimited Tilt
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Solution Overview
Problem
Existing compact double-pass interferometer probe concepts have limited tilt range for the target mirror, which restricts the flexibility and accuracy in applications like lithographic apparatuses where precise positioning and alignment are crucial.
Innovation Solution
The proposed interferometer design features a partially reflective optical component that splits the input radiation beam into two paths, allowing the second path to pass twice between the optical component and a reflective target surface, enabling unlimited tilt range without compromising signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a tilted target mirror is used to prevent single pass interferometer signal being sent back into the input fiber, then the interferometer can operate with a single fiber for input and output, but the tilt range of the target is limited because the first and second reflective surfaces must not coincide
Solution Approach 1:
The optical component is segmented into multiple reflective surfaces (first reflective surface and second reflective surface) that are spatially separated. This segmentation allows the beam to undergo multiple reflections without the first and second reflective surfaces coinciding, thereby enabling unlimited target tilt range while maintaining a compact single-fiber configuration.
Solution Approach 2:
The patent introduces an additional spatial dimension by arranging the first and second reflective surfaces at different locations and orientations. The beam path is extended through multiple reflections between these surfaces, effectively using dimensional separation to prevent surface coincidence and enable unlimited tilt range.
2Reliability
If a beam splitter or optical circulator is used to separate input and output probe radiation, then the interferometer can prevent signal feedback into the input fiber, but the device complexity increases
Solution Approach 1:
The system uses the target mirror itself to perform the function of signal separation. By configuring the optical paths such that the single-pass beam does not return to the input fiber and the double-pass beam is directed to the output fiber, the target mirror serves both as the measurement object and as part of the signal routing mechanism, eliminating the need for additional beam splitters or optical circulators.
3Adaptability or versatility
If the first and second reflective surfaces are arranged to prevent coincidence, then the interferometer can operate with unlimited tilt range, but the optical path becomes more complex
Solution Approach 1:
The patent combines multiple optical functions into a single integrated optical component. The first and second reflective surfaces are incorporated into one component structure, and the beam path is designed to utilize both surfaces sequentially. This merging approach achieves unlimited tilt range while keeping the overall device compact and the optical path manageable.
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 design allows for precise positioning and alignment of targets with unlimited tilt range, enhancing the accuracy and flexibility of interferometer systems in applications such as lithographic apparatuses, while maintaining high fringe contrast and minimizing ghost reflections.
Implementation Method 1
a surface of the optical component is partially reflective and is arranged to reflect a first portion of the input radiation beam to follow a first optical path and is further arranged to transmit a second portion of the input radiation beam to follow a second optical path
Implementation Method 2
the second optical path is directed towards a first location on a reflective target surface and back to the partially reflective surface, then to a second location on the reflective target surface and back to the partially reflective surface
Implementation Method 3
the second optical path is directed through the partially reflective surface to be recombined with the first optical path to provide to a recombined optical path configured to provide an output radiation beam
Data Source
AI summary
A compact dual pass interferometer for a plane mirror interferometer configured to receive an input radiation beam from a light source. An optical component has a partially reflective surface arranged to reflect a first portion of the input radiation beam to follow a first optical path directed towards an output terminal and further arranged to transmit a second portion of the input radiation beam to follow a second optical path, directed towards a first location on a reflective target surface and back to the partially reflective surface, then to a second location on the reflective target surface and back to the partially reflective surface, whereupon the second optical path is directed through the partially reflective surface to be recombined with the first optical path to provide a recombined optical path configured to provide an output radiation beam. The output terminal configured to deliver the output radiation beam to a detector.