Common zeros in synchronization of high-precision stage systems

In synchronization of high-precision motion systems, in particular the synchronization between a wafer stage system and a reticle stage system of a wafer scanner, a novel feedforward structure is studied. In this structure, the numerator of each plant model is described by an input shaping filter capturing the zeros of said model. The denominator is described by a feedforward filter capturing the poles. Ideally, this gives zero error tracking of both the reticle and wafer stage systems without the need for plant inversion. But in view of the different input shaping filter operations, appropriate synchronization behavior is not guaranteed. To obtain both appropriate tracking and synchronization behavior, we propose to augment the reticle stage filters with the zeros from the wafer stage plant model. Reversely, the wafer stage filters are augmented with the zeros from the reticle stage plant model. The feasibility of such an approach is confirmed by simulation results and, to some extend, by measurement results obtained from an industrial wafer scanner.