Numerical Modeling and Method of Air Bearing-based Vibration and Noise Mitigation

Vibration and noise controls are critical in precision optical measurement systems. Highly tight deflections of the specimen are usually enforced to ensure accuracy of metrology. To mitigate impacts of noise sources within the system and from environment, it would require innovative designs of vibration isolation and enclosure setups. Only limited contacts are allowed along the narrow edge when the optics of the surfaces is of interest. It is challenging to maintain nanometer deflections of the specimen during measurement with only mechanical edge constrains. The paper describes a novel air bearing fixture design for holding, compensating and stabilizing circular substrates. A structural finite element analysis (FEA) model was developed and validated for evaluating natural frequencies and static deflection of substrates at different loading positions. Then different air bearing concepts were simulated by introducing elastic foundation stiffness within the FEA model. Computational fluid dynamics (CFD) models were further developed to analyze flow velocity and pressure distributions within the cavity and on the substrates. Design performance was evaluated by integrating with Fizeau optical elements of a dual opposed facing Fizeau interferometer system. Testing results showed improved stabilization of a substrate with vibration amplitude of 1.0 nm over 4 consecutive 30 second measurements.