Robust control of lithographic process in semiconductor manufacturing

In this paper, a stability analysis is conducted for several feedback controllers of photolithography processes. We emphasize the stability of process controllers in the presence of model mismatch, and other uncertainties such as system drift and unknown noise. Real data of critical dimension (CD) in shallow trench isolation area from an Intel manufacturing fab is used for model analysis. The feedbacks studied in this paper include a controller based on an adaptive model, and several controllers based on existing estimation methods such as EWMA, extended EWMA, and d-EWMA. Both theoretical analysis and computer simulations are presented to show the stability of the controlled process under these feedbacks.