Adaptive Cautious Regularized Run-to-Run Controller for Lithography Process

Photolithography is the bottleneck for quality improvement in semiconductor manufacturing processes. The decreasing critical dimensions of the semiconductor product requires more effective run-to-run control technology. Currently, Exponential Weighted Moving Average (EWMA) control scheme is widely used in the overlay control of lithography processes. In this article, we address three shortcomings of the current EWMA run-to-run control scheme: (i) the weight parameter λ used in the EWMA control scheme is set as a fixed value instead of adjusted adaptively according to the process changes; (ii) the conventional EWMA control scheme fails to take the model and parameter uncertainties into consideration; and (iii) the adjustable range of the control variables is not considered in the conventional EWMA control scheme. To meet tighter overlay specifications, we propose a new adaptive run-to-run control scheme to address these three limitations. The effectiveness of the new controller is validated through simulation studies.