Optical Measurement System Cyclic Error Calibration Without Moving Target
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Solution Overview
Problem
Existing methods for calibrating optical measurement systems, such as interferometers in lithographic apparatuses, require a moving target to determine corrective values for cyclic errors, which is not feasible for systems without a moving target.
Innovation Solution
A method and system for calibrating optical measurement systems that utilize two optical axes with different optical path lengths, allowing for the measurement of cyclic errors without the need for a moving target by changing the wavelength of measurement beams and determining corrective values based on these measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a moving target is used to determine corrective values for cyclic errors, then the calibration can be performed, but the method cannot be applied to systems without a moving target
Solution Approach 1:
The patent changes the wavelength parameter of the measurement beam to enable cyclic error determination. By measuring at multiple wavelengths and comparing the results, the system can determine cyclic errors without requiring a moving target, thus resolving the contradiction between system adaptability and measurement precision
2Measurement precision
If the second position is at a distance from the first position in the measuring direction, then the cyclic error can be determined, but the method requires a moving target which limits applicability
Solution Approach 1:
Instead of changing the position of the target (which requires a moving target mechanism), the patent changes the wavelength parameter of the measurement beam. This approach determines cyclic errors by comparing measurements at different wavelengths while keeping the target stationary, thereby reducing device complexity while maintaining measurement precision
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 accurate correction of cyclic errors in optical measurement systems without the requirement of a moving target, improving the precision of position measurements and pattern projection in lithographic processes.
Implementation Method 1
The interferometer system is arranged to accurately determine the position of an object... A measurement error of the interferometer causes the control system to move the object to a location at an offset of the desired position
Data Source
AI summary
The invention provides a method for calibration of an optical measurement system, which may be a heterodyne interferometer system, wherein a first optical axis and a second optical axis have a different optical path length, the method comprises: ∘measuring a first measurement value along the first optical axis using a first measurement beam, ∘measuring a second measurement value along the second optical axis using a second measurement beam, ∘changing a wavelength of the first measurement beam and the second measurement beam, ∘measuring a further first measurement value along the first optical axis using the first measurement beam with changed wavelength, measuring a further second measurement value along the second optical axis using the second measurement beam with changed wavelength, ∘determining a cyclic error of the optical measurement system on the basis of the measured values, and ∘storing a corrective value based on the cyclic error.