Lithographic Stage System Active Stiffness Control
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Solution Overview
Problem
The existing stage systems in lithographic apparatuses face limitations in increasing acceleration without compromising stiffness, leading to reduced positioning accuracy due to the large mass of the stage, which results in undesired vibrations and excitation modes.
Innovation Solution
A stage system with multiple actuators and sensors that measure position-dependent parameters, allowing for the adjustment of stiffness through controller output signals to reduce vibrations and increase acceleration by actively damping resonance modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the mass of the stage is reduced, then the acceleration of the stage can be increased, but the stiffness of the stage decreases leading to undesired vibrations and reduced positioning accuracy
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the stiffness of the stage structure through active control. The system modifies structural parameters in real-time to achieve high stiffness during positioning operations while allowing mass reduction for higher acceleration, resolving the contradiction between speed and strength
Solution Approach 2:
The patent replaces passive mechanical stiffness with active control mechanisms. Instead of relying solely on mechanical structure stiffness, the system uses control algorithms and actuators to maintain positioning accuracy, enabling mass reduction while preserving effective stiffness through substitution of mechanical properties with controlled systems
2Use of energy by moving object
If the mass of the stage is reduced, then less power is needed to accelerate it, but positioning accuracy deteriorates due to vibrations and excitation modes
Solution Approach 1:
The patent substitutes mechanical mass with controlled system dynamics. By using active control and multiple actuators, the system achieves accurate positioning with reduced mass, replacing the need for heavy mechanical structures with intelligent control mechanisms that compensate for vibrations and maintain precision
3Speed
If more powerful actuators are used to increase acceleration, then the acceleration of the stage increases, but the system becomes more complex and requires more energy
Solution Approach 1:
The patent applies multi-functionality by designing actuators that serve multiple purposes: positioning the stage, adjusting structural stiffness, and suppressing vibrations. This universal approach allows achieving high acceleration without requiring separate specialized actuators, thereby reducing overall system complexity while maintaining performance
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 dynamic performance by increasing bandwidth, reducing mass, and improving accuracy while maintaining high stiffness, allowing for higher accelerations and faster settling times.
Implementation Method 1
the actuators adjust the stiffness of the stage based on the further control output signal
Implementation Method 2
a position dependent parameter and an undesired excitation mode or vibration of the stage can be detected by the sensors
Data Source
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AI summary
A stage system for a lithographic apparatus includes a stage, an over-determined number of actuators to act on the stage, at least two sensors to measure a position dependent parameter of the stage and to provide a respective sensor signal. The at least two sensors are arranged to measure the respective position dependent parameters in a same degree of freedom. A controller is provided to provide a controller output signal to at least one of the actuators in response to a setpoint and the position dependent parameter as measured by at least one of the sensors. A further controller is provided with the position dependent parameters measured by the sensors. The further controller is configured to determine a difference between the position dependent parameters from the sensors and to provide a further controller output signal to at least one of the actuators in response to the determined difference.