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Benchmark comparison of multiple process control strategies for lithographic CD control

In this paper, we present a study on the robustness comparison of several process feedbacks controllers. The feedbacks include those based on either EWMA or Kalman Filter estimation. In addition, a new multiple dimension feedback controller is introduced, which has a significantly improved robust stability and reduced sensitivity to unknown noise. In the robustness study, we assume model mismatch and unknown disturbances. Two issues of robustness are addressed in this paper, namely the region of model mismatch in which a process feedback is stable; and the H-infinity gain of the controlled process from unknown noise to the system performance. Simulations are shown to compare the performance of the feedbacks under model mismatch, system drifting, and random noise.