Real-time feedback control of reactive ion etching

This paper explores the application of modern feedback control technology to the regulation of the reactive ion etching process. Currently, this process is run open-loop, except for the PID controller to regulate pressure. We investigate the utility of additional measurements for the purpose of feedback control to improve process performance and robustness. First, we compare a feedback controller that regulates V bias and chamber pressure to one that regulates V bias and fluorine. We show that the fluorine controller yields better control of etch rate; this result is to be expected since fluorine is more closely related to the chemical etching process than is pressure. Our second study compares various controllers that regulate V bias and fluorine using the conductance throttle and applied RF power. We show that multivariable feedback controllers that can compensate for process coupling by coordinating control inputs have advantages over decentralized controllers consisting of two independent feedback loops.