Interferometry Noise Reduction via Intensity Monitoring
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Solution Overview
Problem
Displacement-measuring interferometry systems in precision engineering, such as microlithography exposure systems, face limitations in accuracy due to spectrally dependent intensity fluctuations from broadband light sources, which are not effectively accounted for in current technologies.
Innovation Solution
A broadband displacement-measuring interferometry system that includes a spectrally broadband light source, sensor modules with interferometers, intensity monitors to measure light intensity fluctuations, and an electronic processing module to correct for these fluctuations, enabling precise position monitoring of objects in microlithography systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If broadband light source is used for displacement measuring interferometry, then the measurement range and robustness are improved, but spectrally dependent intensity fluctuations occur which limit measurement accuracy
Solution Approach 1:
An intensity monitor is introduced as an intermediary device that measures the intensity of light from the broadband source independently of the interferometer. This monitor provides feedback about intensity fluctuations, which are then used to correct the interferometer measurements, thereby compensating for the harmful intensity variations while maintaining the benefits of broadband light
Solution Approach 2:
The system implements a feedback mechanism where the intensity monitor continuously monitors light intensity from the broadband source and feeds this information back to the electronic processing module. The processing module uses this feedback to correct interferometer measurements in real-time, compensating for intensity fluctuations and maintaining measurement accuracy
2Measurement precision
If intensity monitor is added to measure and correct intensity fluctuations, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The intensity monitor is designed to serve multiple functions: it characterizes the spectral distribution of the broadband source, monitors intensity fluctuations, and provides correction data for the interferometer measurements. This multi-functionality justifies the additional component by providing comprehensive light source characterization and correction capabilities
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 enhances the accuracy of position monitoring in microlithography exposure systems by compensating for intensity fluctuations, achieving sub-nanometer precision and improving the reliability of next-generation sensors.
Implementation Method 1
at least one sensor module comprising an interferometer configured to receive light derived from the source, direct portions of the light along separate paths, and subsequently recombine the portions of light
Implementation Method 2
each sensor module further comprises a detector configured to measure the recombined light portions and produce a sensor output signal
Implementation Method 3
at least one intensity monitor, each intensity monitor comprising a detector configured to measure the intensity of additional light derived from the source and produce a monitor output signal
Data Source
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AI summary
An interferometry system for monitoring changes in the position of an object, the system includes a spectrally broadband light source, a sensor module having an interferometer that direct portions of the light received from the source along separate paths. The system includes an intensity monitor having a detector configured to measure the intensity of additional light derived from the source and to produce a monitor output signal. The system includes an electronic processing module to process a sensor output signal based on the monitor output signal to account for intensity fluctuations in light output by the source, and determine information about the changes in the position of the object. The intensity monitor is configured to characterize the intensity fluctuations as a function of wavelength or intensity fluctuations that are spectrally correlated.