Multivariable decoupling control system design for the plasma etching process

A multivariable decoupling control system has been developed for the SF₆/Argon plasma etching of silicon (Si) and silicon dioxide (SiO₂) in this work. The singular value decomposition (SVD) technique is employed to determine the pairings between performance quantities, process and manipulated variables based on steady state regression analysis of the system. The SVD pairings with input and output structural compensators designed also by using SVD technique form a multivariable decoupled control system. Non-intrusive techniques are found to very rarely change the variable pairings. Results presented in this paper show that the closed loop transient responses for SVD pairings with the structural compensated MIMO (multi input-multi output) control strategies are typically much faster than the conventional scheme. Both of the control strategies satisfy the robustness requirements but the robust stability of conventional control is worse and the structurally compensated scheme is less sensitive to input perturbations