Wafer Stage Vertical Position Initialization Using Absolute Feedback
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing photolithography tools face challenges in maintaining precise vertical positioning of the wafer stage due to susceptibility to pressure fluctuations and load disturbances, leading to significant deviations and reduced motion precision, primarily because of the absence of absolute zero-position references.
Innovation Solution
The implementation of a fine-motion module with absolute-position sensors to measure and adjust gravity compensator pressures, combined with relative-position sensors for precise control, and the use of feedback control loops to achieve accurate vertical zeroing and initialization of the wafer stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If gravity compensators are controlled using pressure control loop without absolute position feedback, then the structure remains simple, but the initial vertical position becomes significantly susceptible to pressure fluctuations and load disturbances
Solution Approach 1:
The patent introduces absolute position sensors (such as eddy current sensors or capacitive sensors) that provide feedback on the actual vertical position of the wafer stage. This feedback is fed to the controller which adjusts the gravity compensator pressures to maintain the stage at the correct vertical position, thereby eliminating the susceptibility to pressure fluctuations and load disturbances while keeping the system relatively simple.
2Object-affected harmful factors
If the rigidity of gravity compensators is reduced to block low-frequency vibrations, then vibration transmission is reduced, but deviations in initial vertical position increase due to pressure fluctuations and load disturbances
Solution Approach 1:
The low-rigidity gravity compensators allow vibration isolation while the absolute position feedback system continuously monitors and corrects any position deviations caused by pressure fluctuations or load changes. The controller adjusts compensator pressures in real-time to maintain precise vertical positioning despite the reduced rigidity.
Solution Approach 2:
The gravity compensators are designed to counterbalance the weight of the wafer stage, providing support while maintaining low rigidity for vibration isolation. The active pressure control system dynamically adjusts the counterbalancing force to compensate for disturbances, ensuring position accuracy is maintained.
3Measurement precision
If vertical zero-position references are added to the wafer stage, then initialization accuracy and position stability improve, but device complexity increases
Solution Approach 1:
Absolute position sensors provide continuous feedback on the vertical position of the wafer stage relative to a defined zero position. The controller uses this feedback to automatically adjust gravity compensator pressures, maintaining accurate vertical positioning without requiring complex mechanical reference structures. The system achieves high measurement precision through electronic sensing and active control.
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 enhances the stability of the wafer stage's vertical zero position, improves initialization accuracy, and reduces deviations, thereby addressing the reliability issues associated with low vertical motion precision.
Implementation Method 1
a plurality of absolute-position sensors, configured to measure an absolute position of the fine-motion plate and to adjust pressures in the plurality of gravity compensators based on the obtained absolute-position measurements
Implementation Method 2
a plurality of gravity compensators, each having one end fixed on the base and the other end configured to support the fine-motion plate
Implementation Method 3
adjust pressures in the plurality of gravity compensators based on the obtained absolute-position measurements
Implementation Method 4
a plurality of relative-position sensors, configured to measure a relative position of the fine-motion plate to the base and to control the fine-motion plate based on the obtained relative-position measurements
Data Source
AI summary
A fine-motion module for use in a wafer stage of a photolithography tool includes: a base (201); a fine-motion plate (210); a plurality of vertical motors (203), fixed between the base and the fine-motion plate; a plurality of gravity compensators (202), each having one end fixed on the base and the other end configured to support the fine-motion plate; a plurality of absolute-position sensors (205, 211), configured to measure an absolute position of the fine-motion plate and to adjust pressures in the gravity compensators based on the obtained absolute-position measurements such that the absolute position of the fine-motion plate is changed to a predetermined initial vertical position; and a plurality of relative-position sensors (204, 207), configured to measure a relative position of the fine-motion plate to the base and to control the fine-motion plate based on the obtained relative-position measurements, thereby moving the fine-motion plate to a relative zero position.