Hybrid Interferometer Encoder Stage Position Control
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Solution Overview
Problem
Current exposure apparatuses face challenges in achieving high precision and stability in stage position control due to measurement errors from air fluctuations and mechanical instability, particularly when using laser interferometers and encoders in lithography processes for semiconductor and microdevice manufacturing.
Innovation Solution
A movable body drive method that synthesizes signals from a high pass filter and a low pass filter, combining the high linear measurement of interferometers with the high reproducibility of encoders, to drive the movable body based on either the high pass filtered signal at higher frequencies or the low pass filtered signal at lower frequencies, ensuring accurate and stable position control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a laser interferometer is used for position measurement, then measurement stability is improved, but measurement precision deteriorates due to air fluctuation and temperature gradient
Solution Approach 1:
The patent combines two different measurement systems (laser interferometer and encoder) into a hybrid measurement system. The interferometer provides stable long-term measurements while the encoder provides precise short-term measurements, and their signals are synthesized to achieve both stability and precision simultaneously.
Solution Approach 2:
The patent changes the measurement parameters by using different measurement principles for different time scales or frequency ranges. The interferometer operates continuously for stability while the encoder provides high-resolution measurements, and signal processing techniques combine these different parameter regimes.
2Measurement precision
If an encoder is used for position measurement, then measurement reproducibility is improved, but linearity deteriorates due to mechanical instability of the scale
Solution Approach 1:
The patent merges the encoder system with the interferometer system to compensate for the encoder's mechanical instability. The interferometer's stable measurements correct the drift and non-linearity in the encoder's scale, while the encoder maintains its high reproducibility for frequent measurements.
Solution Approach 2:
The interferometer acts as an intermediary reference system that mediates the mechanical instability of the encoder scale. By using the interferometer's stable optical path as a reference, the encoder's measurements are corrected for drift and thermal expansion effects.
3Measurement precision
If hybrid measurement methods are used to improve position control accuracy, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent segments the measurement function into two distinct systems with different strengths: the interferometer handles long-term stability and the encoder handles short-term precision. This segmentation allows each system to be optimized for its specific function while working together through signal synthesis.
Solution Approach 2:
The hybrid measurement system provides multi-functionality by simultaneously achieving both stability and precision that neither system could achieve alone. The system can operate in different modes depending on the measurement requirements, making it universally applicable to various precision positioning tasks.
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
This approach enables precise and accurate linear movement of the movable body, improving overlay accuracy and pattern formation on the object, while minimizing measurement errors and maintaining stability across varying frequencies.
Implementation Method 1
a first detection signal that has been made to pass through a high pass filter and a second signal which is a second detection signal that has been made to pass through a low pass filter having a cut off frequency which is the same as the high pass filter, the first detection signal corresponding to a position of the movable body obtained by receiving a return beam of a measurement beam via an optical member provided on the movable body
Implementation Method 2
the second detection signal being obtained by irradiating a measurement beam on a diffraction grating provided on a measurement plane parallel to the predetermined plane on one of the movable body and an outside of the movable body and receiving a diffraction beam from the diffraction grating by a measurement system
Data Source
AI summary
A stage is driven (position control) using a hybrid signal which is obtained by synthesizing an output signal of an interferometer (an interferometer system) and an output signal of an encoder (an encoder system) that are made to pass through a high pass filter and a low pass filter, respectively. A cutoff frequency is set to a frequency corresponding to a speed slightly smaller than the speed of the stage at the time of scanning exposure. This allows the stage to be driven using an interferometer whose linear measurement is high at the time of scanning exposure, and using an encoder whose measurement reproducibility is high at the time of stepping.