Six degrees-of-freedom dual-servo stage using magnetic levitation technology

Abstract

Next generation lithography equipment requires high precision stage in high vacuum condition. A magnetic levitation stage with six degrees-of-freedom is considered as a state-of-art technology for high vacuum condition. The non-contact characteristic of magnetic levitation enables high precision positioning as well as no particle generation. To deal with large work-piece such as 450mm wafer, long strokes in horizontal plane will be needed together with magnetic levitation in vertical direction. A dual-servo stage which uses coarse and fine stages is suitable for high precision motion with long strokes. The coarse stage moves long strokes with micro level accuracy while the fine stage is positioned with nano-level accuracy levitating upon the coarse stage and being controlled with six degrees-of-freedom. The compactness of the fine stage enables to achieve high bandwidth. To levitate the fine stage against gravity, z-directional linear active magnetic bearing are widely used. However, if electromagnetic actuators are used only as the bearings, heat is inevitably generated, which deforms the structures and then degrades accuracy of the stage. Thus, a gravity compensating mechanism which does not consume power is required. Best candidate of gravity compensator is a permanent magnetic spring which uses attraction and repulsion of permanent magnets. In this thesis, the long-stroke dual-servo stage which has a 6-DOF magnetic levitation fine stage is designed. For magnetic levitation, a new linear active magnetic bearing is proposed and applied to the dual-servo stage. The proposed linear active magnetic bearing consists of gravity compensation mechanism using Halbach magnet arrays and Lorentz actuators. It is named a Halbach linear active magnetic bearing (HLAMB). The static force generated by the gravity compensation mechanism of HLAMB is basically repulsion and attraction force between permanent magnets. A target magnet is placed between two Halbach magnet arra...