Optical Module Control Circuit for Mirror Deformation Damping
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Solution Overview
Problem
Projection exposure apparatuses face challenges in maintaining stable closed-loop pose control of mirrors due to quasi-static and dynamic deformations caused by parasitic mechanical disturbances, which compromise imaging quality and control stability, particularly in EUV lithography where mirrors are used.
Innovation Solution
A control method and circuit that decomposes sensor signals into pose and deformation components, using additional actuators to damp deformations, allowing independent closed-loop pose and damping controls, and employing observers or multivariable systems to reconstruct deformation states without additional sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional actuators are used to damp deformations, then control stability is improved, but device complexity increases
Solution Approach 1:
The system dynamically switches between rigid body control mode and flexible body control mode based on operating conditions. The control circuit determines whether to use additional actuators for damping deformations or to use only position actuators, making the system adaptable rather than statically complex
Solution Approach 2:
The control approach changes parameters (control mode, actuator engagement) based on detected deformation states. When deformations are detected, the system transitions to a parameter set that includes additional actuators; when stable, it uses a simpler parameter set with position actuators only
2Measurement precision
If sensor signals are decomposed into pose and deformation components, then measurement precision is improved, but processing complexity increases
Solution Approach 1:
The sensor signal is segmented into distinct components: pose components and deformation components. This segmentation allows the control circuit to process each type of information separately and appropriately, improving measurement precision while managing complexity through structured processing
Solution Approach 2:
The control circuit acts as an intermediary that receives raw sensor signals, decomposes them into meaningful components, and then processes each component separately. This intermediary processing layer enables precise measurement while maintaining manageable complexity through systematic signal handling
3Speed
If additional actuators are engaged for damping, then control bandwidth is improved, but energy consumption increases
Solution Approach 1:
The additional actuators are engaged periodically or conditionally rather than continuously. The control circuit activates damping actuators only when deformations are detected or during specific operational phases, reducing unnecessary energy consumption while maintaining high control bandwidth when needed
Solution Approach 2:
The system dynamically adjusts actuator engagement based on real-time conditions. Control bandwidth is enhanced when needed through additional actuators, while energy consumption is reduced by disengaging these actuators during stable operating conditions
Data Source
AI summary
An optical module of an assembly in an optical system comprises an optical element, a first number of position actuators for positioning the optical element, at least one additional actuator for damping deformations of the optical element caused by the parasitic mechanical disturbances, at least one sensor for determining the pose of the optical element, and a control circuit for controlling the optical element. A method comprises acquiring at least one sensor signal relating to the pose of the optical element, decomposing the at least one acquired sensor signal into a signal group having at least one pose component and a signal group having at least one deformation component, positioning the optical element on the basis of the pose components, and damping the deformations on the basis of the deformation components. A control circuit controls an optical element.