Over-Actuated Lithography Stage Resonance Control
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Solution Overview
Problem
Lithographic apparatus stages face challenges in achieving high throughput and accuracy due to the need for high stiffness and low weight, which results in internal structural resonances and long settling times, making it difficult to increase the bandwidth of the closed-loop control system and maintain minimal deformation.
Innovation Solution
An over-actuated stage system with a plurality of electromagnetic actuators, where the current is supplied to coils of multiple actuators from a single power supply, mitigating deformation and improving dynamic performance by counteracting resonance and torsion modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the stage is constructed with high stiffness to avoid resonance modes, then the stage stability improves, but the stage weight increases and settling time increases due to small relative damping of high-stiffness materials
Solution Approach 1:
The patent applies active dynamic control through over-actuation, where multiple actuators are controlled to counteract resonance modes and vibrations in real-time. This allows the stage to maintain stability without requiring excessive static stiffness, thereby reducing weight while achieving the desired dynamic performance through active compensation of vibrational modes.
Solution Approach 2:
The patent changes the control parameters by implementing over-actuation with multiple actuators per degree of freedom, allowing independent control of different vibrational modes. This enables the system to optimize the balance between stiffness and damping by actively adjusting actuator forces to suppress resonance, rather than relying solely on passive mechanical stiffness.
2Measurement precision
If the closed-loop bandwidth is increased to improve servo disturbance rejection and tracking performance, then the control performance improves, but internal structural resonances impose severe constraints on the extent to which the bandwidth can be increased
Solution Approach 1:
The patent implements dynamic control through over-actuation, where multiple actuators are independently controlled to actively suppress resonance modes. This allows the closed-loop bandwidth to be increased beyond the natural resonance frequencies by actively canceling out resonant vibrations, thereby achieving high tracking performance without being constrained by passive structural resonance limits.
Solution Approach 2:
The patent employs feedback control through multiple sensors and actuators that continuously monitor and counteract vibrational modes. This feedback mechanism allows the system to maintain stability at higher bandwidths by detecting and actively compensating for resonance effects in real-time, enabling improved tracking performance without being limited by structural resonances.
3Stability of the object's composition
If more actuators are provided to counteract resonance and torsion modes, then the dynamic performance improves, but the device complexity increases
Solution Approach 1:
The patent applies multi-functionality by using the same over-determined set of actuators for multiple purposes: primary positioning, resonance suppression, and torsion mode counteraction. This unified approach allows a single actuator system to perform multiple functions that would otherwise require separate mechanisms, thereby improving dynamic performance without proportionally increasing device complexity.
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 enhances the dynamic performance of the stage by increasing resonance frequencies, achieving higher bandwidth and reducing settling times, thereby improving servo disturbance rejection and tracking performance.
Implementation Method 1
a plurality of electromagnetic actuators, the actuators arranged to act on the stage
Data Source
AI summary
A stage system for a lithographic apparatus includes a stage, an over-determined number of actuators arranged to act on the stage, and an electric power supply configured to provide a current to the actuators, wherein the current is supplied to a coil associated with a first actuator of the actuators and to a coil associated with a second actuator of the actuators.