Study on control strategy of wafer stage and reticle stage of EUVL

Abstract

For scanning and projection exposure, the image quality is decided by many factors, in which synchronization of wafer stage and reticle stage during exposure is a key one. Extreme Ultraviolet Lithography(EUVL) requires a much higher precision and speed for exposure, so the error that wafer stage tracking the reticle stage must be stringently controlled. This paper mainly deals with the control of the magnetic levitation stages of EUVL. The wafer stage and reticle stage used in EUVL are composed of dual stages respectively, namely a coarse stage and a fine stage, with which long distance and accurate positioning can be achieved. Feedback controllers are employed to compensate the positioning errors and solve the synchronization problem. The wafer stage is defined as the master stage and the reticle stage is defined as the follower stage. The slave stage tracks the master at velocity and acceleration at a required reduction ratio at anytime. To each stage, disturbance force is considered in the stage control loops; therefore the disturbance can be eliminated within the loop.