Interferometric Mirror Pose Detection Using Eigenmode Analysis
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Solution Overview
Problem
Existing methods for determining the pose of mirrors in optical systems, particularly in EUV lithography apparatuses, are limited when an exterior fixed reference is not available, making it difficult to measure mirrors using interferometers from the back side.
Innovation Solution
A method involving a mechanical model of the mirror, interferometric detection of distance changes on the curved mirror surface, and ascertaining eigenmode amplitudes and phases to determine the mirror's pose, using a measuring arrangement with an interferometer and beam shaping unit, allowing control of actuators to damp vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If interferometers with targets are used to measure mirrors from the back side, then six degrees of freedom can be controlled, but an exterior fixed reference must be provided which complicates the system setup
Solution Approach 1:
The patent introduces an intermediary fixed reference (sensor frame) that is integrated into the optical system rather than being external. This sensor frame serves as the reference for interferometric measurement while being part of the system's internal structure, eliminating the need for external fixed references and simplifying the overall setup.
Solution Approach 2:
The patent replaces traditional mechanical target-based interferometric measurement with a method that uses the mirror's own mechanical model and vibration analysis. By measuring temporal changes in distance and analyzing eigenmodes, the system determines mirror pose without requiring physical targets attached to the mirror back side.
2Adaptability or versatility
If mirrors are replaced with interior fixed reference, then system flexibility is improved, but interferometric measurement from the back becomes impossible
Solution Approach 1:
The patent inverts the traditional measurement approach by not measuring the mirror directly from the back side. Instead, it measures temporal changes in distance from the front side and uses vibration analysis of eigenmodes to infer the mirror's pose and position, thereby enabling measurement with interior fixed references.
Solution Approach 2:
The patent changes the measurement parameters from static distance measurements requiring back-side access to dynamic temporal change measurements that can be performed from the front side. By analyzing the time-varying distance changes and eigenmode characteristics, the system achieves pose determination without direct back-side measurement.
3Measurement precision
If vibration damping control is implemented, then measurement accuracy is improved, but system complexity increases due to actuator control requirements
Solution Approach 1:
The patent implements a feedback control system where the measured temporal distance changes and eigenmode analysis provide information about mirror vibrations. This feedback is used to control actuators that apply corrective forces to dampen vibrations, thereby improving measurement accuracy while managing the complexity through systematic control loops.
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 precise determination and control of the mirror's pose without requiring an exterior fixed reference, effectively damping vibrations and improving measurement accuracy.
Implementation Method 1
interferometrically detecting a temporal change of a distance of a point on a curved used mirror surface of the mirror
Data Source
AI summary
A method for determining a position of a mirror of an optical system comprises: a) providing at least one parameter from a mechanical model of the mirror; b) interferometrically detecting a temporal change in a distance of a point of a curved mirror effective surface; and c) ascertaining an amplitude and a phase of N eigenmodes from the temporal change in the distance and the at least one parameter to determine the position of the mirror.