Controller design issues in the feedback control of radio frequency plasmaprocessing reactors

Feedback control has the potential for improving the reliability and perfor mance of radio frequency (rf) plasma processing reactors for microelectroni cs etching, deposition, and cleaning applications. Implementation of real-t ime-control strategies has been slowed by lack of analytic or computational tools to design or optimize systems. To address this need, the virtual pla sma equipment model (VPEM) has recently been developed for investigating is sues related to feedback control in rf plasma processing equipment. The VPE M has been employed to investigate feedback control of inductively coupled plasma processing reactors for polysilicon etching and, in this article, re sults from these studies are used in a discussion of controller design, con trol strategies, and validation of the VPEM. It is demonstrated that respon se surface based controllers best operate in combination with corrections f rom an unstructured controller such as a proportional-integral derivative, which relaxes the inherent rigidity of the model-based controller. Since th e behavior of plasma processing reactors generally changes over time due to , for example, coatings of the walls, it was found advantageous to make the controllers adaptive. (C) 1999 American Vacuum Society. [S0734-2101(99)050 03-4].