Run-to-Run Control of DC-Sputtering Processes
A new nonlinear model is proposed for describing the rela-tionship between the relevant inputs and outputs of a DC-magnetron sputtering system used in a manufacturing line for digital-compact discs and analogous optical data-storage devices. It is shown that the process is inherently 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 is 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 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.