Design of a gain scheduled PID controller for precision stage in lithography

This paper presents a novel PID gain scheduling method using root mean square (RMS) for precise positioning stage in lithography process. Low perturbation in regulating control mode is a very important issue and it largely affects the quality of lithography process. Perturbation during regulation control also called as stage hunting, and usually there is a tendency of decrease, if the control bandwidth is reduced, but in this case, the control system is far weak against a small electrical noise or even structural vibration of the building. In this paper, a gain scheduling control scheme using real time RMS converter chip is proposed to minimize stage hunting and maximize immunity for disturbances. For the test of the proposed control scheme, an air levitated precision stage was designed and used in experiment. Also simulations were conducted by MATLAB to model and analyze the stage and controller. The simulation and experimental results are presented to verify the effectiveness of the proposed control scheme for precision positioning stage compared with conventional PID controller.