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Recently, as technology nodes continue to shrink in the manufacturing of integrated circuits (ICs), performance demands for lithographic scanners have consistently risen. As critical specifications for scanners, both overlay and focus must be limited to the nanometer range. The stage-positioning accuracy along x and y axes directly affects overlay, while the accuracy along z-axis directly influences focus. The moving average (MA) and moving standard deviation (MSD) of position error during exposure can be used to evaluate the stage-positioning accuracy. The reticle and wafer stages of scanners are typically multi-input multi-output(MIMO) motion systems. The interaxis coupling of MIMO motion systems being a significant challenge to achieving high positioning accuracy. The state-of-the-art MIMO control strategy employed for the reticle and wafer stages involves the initial implementation of a decoupling controller to eliminate inter-axis coupling, followed by independent single-input-single-output(SISO) control design for each individual axis. The existing decoupling approaches neglect the influence of force ripple of actuator, which contributes to unsatisfactory decoupling performance. On the other hand, the efficiency of existing decoupling approaches relies on the acceleration of reference trajectory. The reference trajectories for x and y axes during exposure have high speed and acceleration, while z-axis reference trajectory has relatively low acceleration, this results in unsatisfactory decoupling performance for z-axis. In this study, a dynamic decoupling controller is proposed to further reduce the inter-axis coupling. Specifically, the controller's input signal is independent of the reference trajectory. Furthermore, considering the force ripple of actuator, a data-based iterative update algorithm is used to approximate the optimal controller coefficients. The reduction in computational complexity and the convergence properties of the algorithm are demonstrated from a model-based perspective. Numerical simulation and Hardware-in-loop(HIL) testing with established approaches confirm that, within a limited number of iterations, this approach improves z-axis stage-positioning accuracy by over 20%, while maintaining the stage-positioning accuracy of x and y axes. The proposed dynamic decoupling controller benefits on focus performance improvement.
Li et al. (Fri,) studied this question.