Modeling and sliding-mode control of wafer stage in lithrography machines

Permanent magnet linear motors (PMLMs) are widely used in many high precision servo motion platforms, and lithography is a typical application. The reticle stage macro movement subsystem of a lithography machine is a 3-DOF coupling system in X-Y direction which requires carefully modelling and control to achieve high precision. This paper proposes a new modeling method for the 3-DOF PMLM driven coupling system. The modeling method considers the rotation angle of linear motors in X direction to solve the coupling problem and to achieve ultraprecision tracking performance with millimeter accuracy. Furthermore a 3-DOF sliding mode controller is designed to control the proposed model. Finally, the effectiveness of this modeling and control strategy is demonstrated via S-curve tracking simulation, and both the performance of the master-slave with feedforward control structure and the main-main with feedforward control structure are compared. The simulation results show that the tracking errors of PMLMs both in X and Y directions are less than 3 μm, and the rotation angle is less than 25 μrad.