Robust multivariable control of plasma etching of Si and SiO2 in SF6/Argon

This paper presents practical design and analysis methods for the robust multivariable control of a SF₆/Argon plasma etching process of silicon (Si) and silicon dioxide (SiO₂). The solution to this problem involves the use of the structured singular value (SSV), which is found very useful since the model uncertainty due to the nonlinear behaviour of the plasma etching is highly structured. Robust stability and robust performance properties in the presence of structured process uncertainty and disturbances are discussed for this system. Results presented in this paper show that both the structurally compensated and conventional control strategies satisfy these robustness requirements