Robust Synchronization of Motion in Wafer Scanners Using Particle Swarm Optimization

For synchronization of high-precision motion stages, in particular a wafer and a reticle stage combination of an industrial wafer scanner, a centralized controller is optimized using both time- and frequency-domain data. The resulting multi-variable controller, which is designed using a sequential loop closing approach, transmits both the error from wafer-to-reticle as well as from reticle-to-wafer stage. The controller is designed to minimize the synchronization error occurring between the otherwise decentralized control loops of both stage systems. The controller tuning is performed using off-line particle swarm optimization and combines time-domain performance specifications with frequency-domain robustness constraints. The optimized controller demonstrates improved synchronization performance which follows from measurement results obtained from an industrial wafer scanner.