Design of coarse-fine control system for wafer stage of lithography using PQ method

Wafer stage control system of step-scan lithography is a typical dual-stage system. Fine actuator ensures the high tracking precision and coarse actuator makes large-stroke movement to keep the fine actuator is not closed to saturation. PQ method is an effective technique for transforming a DISO system to two SISO systems. Two correlative controllers are designed for the parallel SISO systems which determine the bandwidths of coarse system and fine system, and the relative actuator contribution can be controlled. The third controller is used to ensure that the whole system is stable and the servo bandwidth is high enough. S-curve signal tracking simulation results show that the performance of whole wafer stage control system is satisfactory, and sine signal tracking simulation results show that coarse system and fine system can respectively respond low frequency large-stroke and high frequency short-stroke signal using one closed loop.