Interferometer System for Optical Element Position Monitoring
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Solution Overview
Problem
Precision engineering systems require accurate measurement of object position to nanometer-level tolerances over extended periods, especially in applications like photolithography tools where small range of motion and fine adjustments are necessary, but existing sensors are limited in sensitivity and stability.
Innovation Solution
The development of a fiber sensor system using multiple passive, interferometric optical sensors illuminated by fiber waveguides, which provide continuous, high-speed absolute distance measurements and are insensitive to unwanted degrees of freedom, allowing for precise position monitoring and control of optical components in precision engineering systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional encoder devices are used for position feedback control, then position measurement can be achieved, but measurement precision and stability are limited and cannot maintain nanometer-level tolerances over extended periods
Solution Approach 1:
The patent replaces traditional mechanical encoder devices with an optical interferometry-based measurement system. The interferometric sensors use light wave interference patterns to measure position changes, eliminating mechanical contact and associated wear, friction, and drift issues. This substitution enables nanometer-level measurement precision and long-term stability required for photolithography applications.
Solution Approach 2:
The patent changes the measurement parameter from mechanical position encoding to optical path length interference. By using multiple wavelengths of light and analyzing interference patterns, the system achieves superior measurement precision and stability. The optical parameters (wavelength, interference fringe patterns) provide more accurate and stable position feedback compared to mechanical encoders.
2Measurement precision
If multiple sensors are placed throughout the PO assembly to measure relative positions, then position feedback control is provided, but device complexity increases
Solution Approach 1:
The patent employs a universal interferometric measurement principle that can be applied to multiple measurement points throughout the PO assembly. Instead of using different types of sensors for different measurements, the same interferometric technology measures all relative positions, simplifying the overall system architecture while maintaining high measurement precision across multiple degrees of freedom.
Solution Approach 2:
The patent introduces optical fibers as intermediaries to transmit light between the light source/detector subsystem and the interferometric sensors distributed throughout the PO assembly. This intermediary approach allows remote sensing without adding complex wiring or power delivery systems to each sensor location, reducing overall device complexity while enabling precise multi-point measurement.
3Stability of the object's composition
If active servo loops are used for stability and fine controlled adjustments, then position control is improved, but thermal disruption and system complexity increase
Solution Approach 1:
The patent replaces active servo loops with passive interferometric optical sensors for position measurement. The interferometric sensors provide continuous position feedback without requiring active mechanical adjustment mechanisms, reducing thermal generation from motors and actuators. Position stability is achieved through precise optical measurement and control rather than continuous mechanical actuation.
Solution Approach 2:
The interferometric sensors passively measure position changes without requiring external power or active control at the sensor location. The measurement system itself provides the stability function by continuously monitoring position, eliminating the need for separate active servo mechanisms that generate heat and add complexity.
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
The system achieves high accuracy and reliability in monitoring optical component positions with nanometer-level precision, stability over months or years, and is robust, cost-effective, and minimally disruptive thermally, making it suitable for long-term use in precision engineering applications.
Implementation Method 1
each interferometer configured to derive a first wavefront and a second wavefront from input radiation and combine the first and second wavefronts to provide output radiation including information about an optical path length difference
Implementation Method 2
Each fiber waveguide configured to deliver the input radiation to a corresponding interferometer or deliver the output radiation from the corresponding interferometer to a corresponding detector
Data Source
AI summary
System for monitoring a position of one or more optical elements in a projection objective (PO) include a plurality of sensors each configured to receive input light and to form output light, each sensor including a first sensor optic and a second sensor optic, the first sensor optic of at least one of the sensors being affixed to a first PO optical element and the second sensor optic of the at least one sensor being affixed to a support element that positions the first PO optical element within the PO, the first and second sensor optics being configured introduce a first optical path length difference (OPD) between two components of the input light to form the output light, the first OPD being related to the position of the first PO optical element with respect to the support element. The systems also include a plurality of detectors configured to detect the output light from the sensors, a plurality of optical fibers configured to direct the input light to the sensors and to direct the output light from the sensors to the detectors, and an electronic controller in communication with the plurality of detectors, the electronic controller being configured to determine information about the position of the first PO optical element relative to the support element based on the detected output light from the at least one sensor.