  Growing demands in the semiconductor industry necessitate increasingly
stringent requirements on throughput and positioning accuracy of lithographic
equipment. Meeting these demands involves employing highly aggressive motion
profiles, which introduce position-dependent flexible dynamics, thus
compromising achievable position tracking performance. This paper introduces a
control approach enabling active compensation of position-dependent flexible
dynamics by extending the conventional rigid-body control structure to include
active control of flexible dynamics. To facilitate real-time implementation of
the control algorithm, appropriate position-dependent weighting functions are
introduced, ensuring computationally efficient execution of the proposed
approach. The efficacy of the proposed control design approach is demonstrated
through experiments conducted on a state-of-the-art extreme ultraviolet (EUV)
wafer stage.
