Tuning rule for linear control of nonlinear reactive sputter processes

A tuning rule for the linear control of nonlinear reactive sputter processes is developed based on a process model, which has the form of an Abel differential equation. The process characteristics relates to a supercritical Pitchfork bifurcation with stable and unstable equilibrium states. The paper presents a tuning rule to achieve a desired closed-loop transition behavior and set-point following for step-shaped reference signals without the need of an identified process model. The tuning rule is deduced from the given stability conditions. Experiments are presented for the validation of the developed control structure and the proposed tuning rule. They show that reactive sputter processes can be systematically tuned to achieve a desired closed-loop behavior.