Visco-Elastic Stage Coupling for Lithography Resonance
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Solution Overview
Problem
Lithographic apparatus stage positioning systems face limitations in achieving higher speed and acceleration due to bandwidth constraints imposed by dominant natural frequencies, leading to instability and reduced positioning accuracy.
Innovation Solution
Incorporating a visco-elastic element to couple the first and second bodies of the stage positioning system, which reduces the amplitude of dominant natural frequencies, thereby making the system less sensitive to these frequencies and allowing for improved damping of vibrations, thus enhancing stability and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the stage positioning system operates at higher speed and acceleration to increase productivity, then the bandwidth requirement increases, but the system becomes unstable due to the dominant natural frequency limit
Solution Approach 1:
A coupling is introduced between the actuator and the first body to serve as an intermediary element. This coupling includes a visco-elastic element that filters out the dominant natural frequency from the actuator's output before it reaches the first body, allowing higher bandwidth operation without exciting resonant vibrations that would cause instability
Solution Approach 2:
The visco-elastic element's material properties are specifically selected to have a loss peak at the dominant natural frequency of the first body. By changing the parameters of the coupling element to match the resonant frequency characteristics, the system can operate at higher speeds and accelerations while the coupling automatically dampens vibrations at the critical frequency
2Measurement precision
If the controller bandwidth is increased beyond the dominant natural frequency limit, then higher positioning performance is achieved, but the controller becomes unstable
Solution Approach 1:
The coupling acts as a physical filter between the controller's actuator output and the stage body. It allows the controller to operate with higher bandwidth for improved positioning accuracy while the visco-elastic element in the coupling prevents the transmission of high-frequency commands that would excite the dominant natural frequency and cause instability
3Speed
If a rigid coupling is used between actuator and first body, then the natural frequency is higher, but the system becomes more sensitive to vibrations and resonance
Solution Approach 1:
Instead of using a rigid coupling, a visco-elastic element is employed whose mechanical properties are specifically tuned to the system's dominant natural frequency. This element provides frequency-selective damping that reduces vibration sensitivity at the critical frequency while maintaining adequate stiffness for positioning accuracy
Solution Approach 2:
The coupling is designed to exploit the dominant natural frequency characteristic by placing the visco-elastic element's loss peak at this frequency. What was previously a harmful resonant frequency becomes the target frequency for maximum damping, converting the harmful vibration sensitivity into a controlled energy dissipation mechanism
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 enables increased productivity by allowing higher speed and acceleration while maintaining system stability, improving positioning accuracy and reducing the risk of resonance-induced fatigue, ultimately enhancing the quality of integrated circuits produced.
Implementation Method 1
The coupling comprises a visco-elastic element arranged to couple the first body and the second body to each other
Implementation Method 2
the visco-elastic element is able to reduce an amplitude of a dominant natural frequency of the first body, of the second body or of the dynamical system formed by the first body, the second body and the coupling
Data Source
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AI summary
A stage positioning system (200), comprising a first body (20), a second body (22) and a coupling (24) arranged to couple the first body and the second body to each other. The coupling comprises a visco-elastic element (26) arranged to couple the first body and the second body to each other. The stage positioning system may further comprise a sensor and an actuator. The sensor is to provide a signal representative of a position of the first body. The actuator is to move the first body. The second body is arranged to couple the actuator and the coupling to each other.