A Dual-Servo Stage With 6 D.O.F. Magnetically Levitated Fine Stage

A novel dual-servo stage using the magnetic levitation technology for semiconductor lithography to achieve high-precision and high-acceleration simultaneously is shown in this paper. The dual-servo is one of the methods to realize high-precision with a large stroke. The proposed fine stage magnetically levitates by six degrees of freedom (D.O.F.) and is composed of a coarse stage without mechanical connections. The proposed dual-servo stage is vacuum compatible and cost-effective. A 6 D.O.F. magnetic-levitated fine stage is also proposed for the dual-servo stage. Designed fine stage levitates and actuates using a voice coil actuator with the Halbach magnet array. The magnetic flux is analytically modeled and verified via FEM simulations. Optimization is also performed to determine optimal design values. Two degrees of freedom of the stack type coarse stage are proposed for providing a large stroke and thrust force. Control strategies for the proposed dual-servo stage are introduced. The master-slave type control block diagram is used for overall control. For compensating the reaction force, a force observer is proposed. The sensor kinematics and actuator kinetics are designed. A dual-servo stage is manufactured with optimized design values. For levitating, 6 LVDTs are used for the homing control. After levitating, sensor switching was performed. The out-of-plane motion is fine controlled by 3 capacitance sensors and the in-plane motion is fine controlled by 3 laser interferometers. The moving ranges are 400 mm for the X- and Y-axis. The maximum speed is 175 mm/s, and the in-position stability is ±4.5 nm.