A Design of Plasma Emission Intensity Ratio Control System for a Microwave Plasma CVD Process Using FRIT

We propose a method of designing a FRIT(Fictious Reference Iterative Tuning)-based control system for a microwave plasma CVD(Chemical Vapor Deposition) apparatus used in the preparation of diamond thin films. Specifically, we propose a control system that adjusts the flow rate ratio of CH4 and H2, the material gases, using the spectral emission intensity ratio of the plasma, which affects the film quality, as the controlled variable. We show how to design an experimental apparatus including actuators and sensors for this purpose. The FRIT method, a well-known data-driven control method, is used to design the controller gain from a set of experimental data without modeling complex objectives such as plasma behavior. Through control experiments of the emission intensity ratio, it is shown that the controller gain can be tuned by using a reference model with different time constants to adjust the performance of the response of the control system.