Lithographic Stage Control via Disturbance Torque Estimation
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Solution Overview
Problem
Conventional lithographic apparatus control systems face challenges in accurately maintaining the position of a substrate table within the focal plane due to disturbance torques, which can lead to focus errors and pattern accuracy deterioration, especially when the stage is positioned off-center.
Innovation Solution
A control system that includes a disturbance torque estimator and a correction signal calculator to determine a feedforward correction signal, which corrects position errors caused by disturbance torques, ensuring precise positioning and maintaining the substrate within the focal plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional control system is used to control substrate table position, then the control system is simple and does not require disturbance torque estimation, but position errors occur due to disturbance torques when the stage is positioned off-center
Solution Approach 1:
The disturbance torque estimator estimates the disturbance torque before it significantly affects the position, and the correction signal calculator computes a feedforward correction signal in advance. This preliminary action allows the system to proactively compensate for disturbance torques caused by off-center positioning, preventing position errors before they occur rather than reacting after they occur.
Solution Approach 2:
A correction signal calculator acts as an intermediary component between the disturbance torque estimator and the actuator. This intermediary processes the estimated disturbance torque and generates an appropriate correction signal, mediating the control action to eliminate position errors without requiring complete redesign of the entire control system.
2Area of stationary object
If the substrate table is positioned off-center to access different target portions, then the coverage area increases, but disturbance torques cause position errors in the focal plane
Solution Approach 1:
The system applies a preliminary anti-action by estimating the disturbance torque and generating a correction signal that counteracts the harmful effect before it causes focus errors. The correction signal calculator computes a feedforward correction signal that opposes the disturbance torque's effect on position accuracy, allowing off-center positioning without sacrificing focus accuracy.
3Measurement precision
If feedforward correction is implemented to correct position errors, then position accuracy improves, but the control system complexity increases due to additional components
Solution Approach 1:
The feedforward correction signal is calculated in advance based on the estimated disturbance torque, allowing the system to proactively compensate for position errors before they occur. This preliminary calculation approach improves position measurement accuracy without requiring complex real-time feedback mechanisms or additional sensors.
Data Source
Figure 1
Figure 2~3
Figure 4A~4B
AI summary
A control system to control a position parameter of a stage in a lithographic apparatus includes a stage controller to control a position parameter of the stage in at least a first direction. The control system includes a disturbance torque estimator to estimate a disturbance torque on the stage, the disturbance torque about an axis extending in a second direction, the second direction being substantially perpendicular to the first direction. The control system includes a correction signal calculator, the correction signal calculator provided with the estimated disturbance torque and a signal representative of a position of the stage in a third direction, the third direction being substantially perpendicular to the first and second directions. The correction signal calculator determines a feedforward correction signal to correct a position error of the stage in the first direction due to the disturbance torque, the feedforward correction signal to be fed to the stage.