Interferometer Positioning System with Dual-Frequency Calibration
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Solution Overview
Problem
Current calibration methods for interferometer systems in moving applications are complex and not easily adaptable, requiring simultaneous use of multiple light source frequencies.
Innovation Solution
A positioning system that uses an interferometer system with a first light source emitting at a fixed frequency and a second light source capable of emitting at two different frequencies, allowing the system to determine an absolute position of a moveable target by analyzing phase differences at different frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current calibration methods for moving interferometer applications are used, then absolute position information can be obtained, but the calibration process becomes complex and requires simultaneous use of multiple light source frequencies
Solution Approach 1:
The patent applies periodic action by modulating the second light source to emit at two different frequencies in alternating time periods. During first time periods, the second light source emits at a first frequency, and during second time periods, it emits at a second frequency. This temporal separation allows the system to obtain phase difference information at different frequencies without requiring simultaneous multi-frequency operation, thereby simplifying the calibration process while maintaining the ability to determine absolute position
Solution Approach 2:
The patent changes the frequency parameter of the second light source between two different values (first frequency and second frequency) at different time periods. By varying this critical parameter temporally rather than simultaneously, the system can extract multiple phase difference measurements needed for absolute position determination without the complexity of handling multiple frequencies at once, thus resolving the contradiction between measurement precision and device complexity
2Ease of manufacture
If static calibration methods are used for interferometer systems, then calibration can be performed, but the methods are not suitable for moving applications
Solution Approach 1:
The patent applies dynamics by adapting the calibration method specifically for moving applications. The system measures phase differences while the interferometer is in motion, and uses temporal modulation of light source frequencies to extract absolute position information from dynamic measurements. This dynamic calibration approach maintains ease of calibration while making the system adaptable to moving applications, resolving the contradiction between calibration ease and adaptability
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 easy and effective calibration of the absolute position of a moveable target, improving the accuracy and simplicity of the calibration process in moving interferometer applications.
Implementation Method 1
A first portion of both light beams is tapped off and both first portions are made to interfere, after which the power of the interference result is detected by a reference detector while a second portion of one of the light beams is allowed to travel along a reference path, and a second portion of the other one of the light beams is allowed to travel along a measurement path. Both second portions are made to interfere and the power of the interference result is detected by a measurement detector.
Data Source
AI summary
The invention provides a positioning system to determine an absolute position of a moveable target relative to a reference, comprising an interferometer system with a first light source to emit light at a fixed frequency and a second light source to emit light at at least two different frequencies. The positioning system is configured to determine, based on movement of the target, a phase difference curve associated with a first frequency of the second light source and a phase difference curve associated with a second frequency of the second light source as a function of a phase difference associated with the fixed frequency of the first light source and to determine a cross-point to determine the absolute position of the moveable target. The invention also relates to a lithographic apparatus and corresponding method.