(The) high-precision and high-acceleration dual-servo stage using magnetic levitation technology

Abstract

This paper presents the novel dual-servo stage using magnetic levitation technology for semiconductor lithography has been proposed to perform high precision and high acceleration simultaneously. Dual-servo mechanism is one of the methods to achieve high-precision, high-velocity and time effective. Generally, a dual-servo stage is composed of a coarse stage and a fine stage. The coarse stage has large strokes and capacity for heavy payload while it has low precision. On the other hand, the fine stage has high-precision and fast response with short strokes. Since the fine stage is combined with the coarse stage, dual-servo stage can perform large strokes and high-precision simultaneously. The proposed dual-servo stage is vacuum compatible and cost effective. The magnetic levitated six degrees of freedom fine stage has also been proposed for the dual-servo stage. The proposed fine stage is levitated and actuated using a voice coil motor actuator with the Halbach magnet array. The magnetic flux modeling and optimization are performed to manufacture optimal fine stages. The two degrees of freedom stack type coarse stage has been proposed for providing large stroke and thrust force. Linear motor was used for actuator and linear encoder and LM guide were installed. Control strategies for the proposed dual-servo stage were introduced. The master-slave type control block diagram was used for overall control. For compensating reaction force, force observer was proposed. The time delay control and the proximate time optimal servomechanism control laws were derived and the mode switch control for two different controllers was proposed. The dual-servo stage has been manufactured by using optimized design values. For levitating, six LVDTs were used for homing control. After levitating, out of plane motion was finely controlled by three capacitance sensors and in plane motion was also finely controlled by three laser interferometers. The performances of the manufactured dual-servo stage were evaluated by several categories, such as basic and dynamic performances. The moving ranges are 400mm to both of X and Y axis. The maximum speed is 350mm/s and maximum acceleration is 1G. In position stability is $\pm4.5nm$ and settling time is 45ms when 1mm step reference excited (1% settling).