Planar Motor Torque Cancellation via Counterweight
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Solution Overview
Problem
In lithography processes, planar motors used in moving body apparatuses for exposure systems generate reaction forces that cause vibrations, degrading exposure accuracy due to mechanical friction and torque imbalances.
Innovation Solution
A moving body apparatus with a planar motor system that includes a base with a guide surface, a moving body, and a canceling device comprising a mass body and an actuator to counteract torque around the center of gravity, using orthogonal movement and magnetic fields to minimize vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a planar motor is used to drive the wafer stage, then positioning speed and accuracy are improved and mechanical friction is reduced, but reaction force causes vibrations that degrade exposure accuracy
Solution Approach 1:
A counterweight mechanism is introduced that applies a force in the opposite direction to the reaction force generated by the planar motor. This counterbalancing force cancels out the vibrations caused by the reaction force, allowing the planar motor to maintain its high positioning accuracy while eliminating the harmful vibrations that would otherwise degrade exposure accuracy.
Solution Approach 2:
The reaction force, which is initially a harmful factor causing vibrations, is converted into a useful force by the counterweight mechanism. The counterweight uses the reaction force as input and generates a beneficial counteracting force that stabilizes the system, transforming the harmful vibration source into a component that actively contributes to vibration cancellation.
2Device complexity
If a planar motor is used to drive the wafer stage, then the configuration is simplified and running cost is reduced, but torque imbalance degrades exposure accuracy
Solution Approach 1:
The counterweight mechanism compensates for torque imbalance generated by the planar motor by applying an equal and opposite torque. This allows the simplified planar motor configuration to maintain its advantages of reduced complexity and cost while the counterweight actively corrects the torque imbalance that would otherwise compromise exposure accuracy.
Solution Approach 2:
The system incorporates feedback control that monitors the torque output of the planar motor and adjusts the counterweight mechanism accordingly. This feedback loop detects torque imbalance and dynamically adjusts the counteracting force to maintain precise exposure accuracy, enabling the simplified configuration to achieve high precision through active compensation.
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 solution effectively reduces vibrations and improves exposure accuracy by canceling torque and minimizing mechanical friction, enhancing the precision of pattern transfer in semiconductor and liquid crystal display device fabrication.
Implementation Method 1
a planar motor that comprises a first member that is provided to the base and a second member that is provided to the moving body and that, through the cooperation of the first member and the second member, generates a thrust between the base and the moving body
Implementation Method 2
a canceling device that, when the moving body moves owing to the thrust of the planar motor, applies a force to the base in a direction that cancels a torque generated around the center of gravity of a system that includes the base and the moving body
Implementation Method 3
a mass body, which moves in an orthogonal axial direction, which is a direction orthogonal to the guide surface; an actuator that moves the mass body with respect to the guide in accordance with the movement of the moving body
Data Source
AI summary
When a wafer stage WST accelerates and decelerates on a base, a torque that acts on a wafer drive system including the base and the like is cancelled out by a torque that acts on the wafer drive system by driving a counter of a coutermass device along a linear guide in the Z-axis direction at a predetermined acceleration. Thereby, the torque that acts upon the wafer drive system is cancelled and the exposure apparatus can expose the wafer with good accuracy.