Rapid Precision Positioning with Transition-Positioning Switching in Stepper Lithography

In stepper lithography, the motion control consists of precision positioning concatenating with output transition of the wafer in a step-by-step rastern pattern. Rapid precision positioning becomes challenging as post-transition vibrations can be induced after each transition, and the precision of the wafer positioning can be adversely affected by the transition-to-positioning switching and the drift of the motor system. The main contribution of this paper is the development of a technique that combines an optimal transition trajectory design with the iterative-learning-based feedforward-feedback control. The optimal transition trajectory design method is utilized to obtain the desired trajectory for rapid stage transition without inducing post-transition vibration of the wafer stage when reaching the exposure position. Then a modeling-free iterative-learning control technique is employed to track the desired transition trajectory accurately, and integrated with feedback control through set-point tuning to remove zero-drift during the positioning. This integrated method is illustrated by implementing it to the motion control in a stepper lithography. The experimental results demonstrate the efficacy of the proposed approach over conventional method in achieving rapid precision positioning for stepper lithography.