Automatic Microwave Tuner for Plasma Deposition Applications Using a Gradient Search Method

This paper describes a practical realization of an automatic microwave matching unitfor an electron cyclotron resonance plasma enhanced chemical vapor deposition system. The matching unit includes a waveguide section with three screw stubs controlled by stepper motors. By using only information about the reflected power, a matching algorithm based on the method of steepest descent moves the stubs in such a way as to minimize the reflected power. The same program controls gas flows, magnetic field and forward microwave power to enable growth of dielectric layers of the desired composition profile for optical applications.