Lithographic Stage Position Measurement with Sensor Discrepancy Correction
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Solution Overview
Problem
In lithographic apparatuses, position measurement inconsistencies due to sensor drift and thermal fluctuations lead to offset errors, alignment issues, and overlay errors, particularly when different subsets of sensors are activated at varying stage positions relative to reference plates.
Innovation Solution
A stage system with a movable stage and a position measurement system that includes a reference plate and multiple sensors, where a processor determines the stage position from an over-determined number of sensor signals and corrects discrepancies between sensor signals to ensure accurate positioning, and a correction method that involves measuring and displacing stages in both measurement and exposure areas to determine correction factors for scaling the position measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple sensors are used to measure stage position at different locations, then measurement coverage is improved, but measurement consistency deteriorates due to sensor drift and thermal fluctuations
Solution Approach 1:
The patent combines measurements from multiple sensors (at least three sensors) to determine stage position. By merging the sensor signals and using a common reference plate, the system achieves both wide measurement coverage and consistent measurements across different sensor locations, resolving the contradiction between coverage area and measurement consistency.
Solution Approach 2:
The system uses feedback from multiple sensors to continuously monitor and correct stage position measurements. The processor compares measurements from different sensors and applies corrections based on the common reference plate, ensuring measurement consistency while maintaining wide coverage through multiple sensor positions.
2Adaptability or versatility
If different subsets of sensors are activated at varying stage positions, then adaptability is improved, but measurement accuracy deteriorates due to offset errors and alignment issues
Solution Approach 1:
The patent implements a universal reference plate that serves all sensor positions. This common reference structure enables any sensor subset to measure against the same reference, ensuring measurement accuracy is maintained regardless of which sensors are active or which stage position is being measured, thus achieving both adaptability and precision.
Solution Approach 2:
The system dynamically adjusts measurement parameters by selecting appropriate sensor subsets based on stage position while maintaining measurement accuracy through the common reference plate. The processor modifies which sensors are used (parameter change) based on position, but the reference framework ensures accuracy is preserved across all configurations.
3Reliability
If sensor signals are corrected for thermal expansion and drift, then measurement reliability is improved, but system complexity increases
Solution Approach 1:
The patent introduces a common reference plate as an intermediary between the sensors and the stage. This reference plate provides a stable reference frame that simplifies the correction process, as all sensor measurements are referenced to the same stable object, reducing the complexity of compensating for thermal expansion and drift compared to using multiple independent references.
Data Source
AI summary
A position measurement system to measure a position of a movable stage includes a reference plate; a plurality of sensors arranged such that, depending on a position of the movable stage relative to the reference plate, at least a subset of the plurality of sensors is configured to cooperate with the reference plate to provide for each of the sensors in the subset respective sensor signals representative of a position of the respective sensor relative to the reference plate; and a processor arranged to determine from the sensor signals a stage position, the processing device configured so as to, when the stage is in a position where an over-determined number of sensor signals is provided by at least the subset of the sensors that are in operational cooperation with the reference plate, (a) determine the stage position from a subset of the over-determined number of sensor signals, and (b) correct a sensor signal of one or more of the sensors from a discrepancy between the determined stage position and a remainder of the sensors signals.