Run-to-run control of DC-sputtering processes

A nonlinear model is proposed for describing the relationship between the relevant inputs and outputs of a DC-magnetron sputtering system used in a manufacturing line for digital-compact discs and other optical data-storage devices. It is shown that the process is intrinsically discrete, and that it has an inherent transport delay. A control scheme is proposed consisting of a Smith predictor to address the delayed dynamics, and a globally linearizing operator introduced to address the nonlinear nature of the model. The control structure requires knowledge of two model parameters, namely, the maximum film reflectivity and the characteristic-energy factor of the sputterer and makes use of one tuning variable, namely, the parameter of an integral-only controller. The performance of the control system is illustrated via a simulation study