Heterodyne Interferometer Cyclic Error Calibration
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Solution Overview
Problem
Existing interferometer systems in lithographic apparatuses suffer from cyclic errors due to limitations in measuring object position accuracy, particularly in methods requiring smooth movement over large ranges or vibrating at specific frequencies, which can be disturbed by system dynamics and sampling frequencies.
Innovation Solution
An interferometer system utilizing a heterodyne interferometer with a processing system that generates reference and measurement signals with specific phases and amplitudes to determine cyclic errors, and an optical measurement system that uses multiple wavelength radiation beams to calculate distance differences, enabling accurate correction of cyclic errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the object moves with a specific speed over a specific range to determine cyclic errors, then the cyclic errors can be determined, but the movement may be disturbed by vibrations and the movement range may not be sufficiently long
Solution Approach 1:
The patent applies mechanical vibration by causing the object to vibrate at a certain frequency and amplitude to determine cyclic errors. This vibration-based approach allows cyclic error measurement without requiring large-range smooth movement, thereby avoiding vibration disturbances and insufficient movement range issues while maintaining measurement accuracy
2Measurement precision
If the object vibrates with a certain frequency and amplitude to determine cyclic errors, then the cyclic errors can be determined, but the choice of frequency is limited due to system dynamics and sampling frequencies
Solution Approach 1:
The patent employs dynamics by enabling the object to vibrate at optimized frequencies and amplitudes that are adapted to the specific measurement conditions and object properties. This dynamic approach allows flexible frequency selection based on system characteristics rather than being constrained by fixed frequency requirements, thereby improving both measurement accuracy and frequency selection flexibility
3Measurement precision
If the interferometer system is used to accurately determine object position, then the pattern can be projected properly, but cyclic errors cause the object to move to an offset location
Solution Approach 1:
The patent implements feedback by using the determined cyclic error information to correct the interferometer measurements in real-time. The cyclic errors are characterized through vibration-based measurement and then applied as correction factors to compensate for position offsets, ensuring that the control system accurately positions the object for proper pattern projection despite the presence of cyclic errors
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 proposed solution improves interferometer accuracy by effectively determining and correcting cyclic errors, ensuring precise object positioning and pattern projection in lithographic processes, independent of movement speed and frequency constraints.
Implementation Method 1
an heterodyne interferometer; a processing system, wherein the heterodyne interferometer is arranged to provide a reference signal and a measurement signal, wherein the reference signal has a reference phase, wherein the measurement signal has a measurement phase and an amplitude
Implementation Method 2
the interferometer system provides a repetitive signal based on the position of the object. The cyclic errors are errors of the repetitive signal that depend on the phase of the signal
Implementation Method 3
the interferometer is arranged to provide a first distance signal representative of a distance to a target, wherein the interferometer is arranged to provide a second distance signal representative of the distance to the target, wherein the first distance signal is based on a radiation beam with a first wavelength, wherein the second distance signal is based on a radiation beam with a second wavelength
Data Source
AI summary
An interferometer system, including a heterodyne interferometer and a processing system. The heterodyne interferometer is arranged to provide a reference signal and a measurement signal. The reference signal has a reference phase. The measurement signal has a measurement phase and an amplitude. The processing system is arranged to determine a cyclic error of the heterodyne interferometer based on the reference phase, the measurement phase and the amplitude.