Application of feed-forward control to a lithography stepper

Presents a novel feedforward control algorithm that seeks to improve the reproducibility of pattern transfer in modern photolithography process sequences. Coupled with a feedback controller and accurate empirical equipment models, the feedforward controller significantly improves the process capability index (Cpk) of the lithographic sequence by centering its response around the specifications and by reducing its inherent variance. This algorithm has been implemented on a resist coat and expose sequence in the Berkeley Microfabrication Laboratory. Experimental results show that process accuracy can be significantly improved by the application of this algorithm.<
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