Iterative and Real-Time Trajectory Modification Control via Error Decoupling for Wafer Scanner Synchronization

In wafer scanners, synchronization accuracy between the wafer stage and reticle stage (RS) directly determines exposure quality. Existing main–secondary control methods face three challenges. First, the measured synchronization error inherently couples the RS tracking error and main–secondary error, making precise compensation difficult. Second, existing methods based on model inversion or iterative feedforward approaches exhibit limited capability in suppressing inevitable external disturbances. Third, directly modifying existing servo control loops is often impractical due to proprietary control architectures. To address these challenges, this article proposes iterative and real-time synchronization trajectory modification control (IRSTMC), achieving high-precision synchronization tracking and disturbance rejection without altering the original servo control loop. The method features three key innovations. First, a time-frequency analysis-based decoupling technique is developed to predict RS position and extract the dominant main-secondary error, establishing the foundation for precise compensation. Second, a unified dual-module scheme integrating iterative synchronization trajectory modification (ISTM) and real-time synchronization trajectory modification (RSTM) is proposed, where ISTM compensates tracking errors through iterative learning and RSTM suppresses stochastic disturbances through real-time correction via external synchronization feedback. Third, unlike existing trajectory compensation methods requiring predefined references, IRSTMC enables trajectory modification for real-time generated references. Experimental validation demonstrates that IRSTMC achieves 65% improvement over the baseline method and significantly outperforms existing approaches in synchronization accuracy.