The problem of designing a robust controller to solve a tracking control problem for improving plasma characteristics in Reactive Ion Etching Systam is studied. The presented design methodology is based on the construction of a two-time scale motions of the closed-loop system. It has been shown that a sufficiently small perturbation parameter associated with the dynamical controller consisting of high order derivatives of the output signal, induces a two time-scale separation of the fast and

more »

... w modes in the closed-loop system. Stability conditions imposed on the fast and slow models can ensure that the fullorder closed-loop system achieves the desired properties so that the output transient performances are insensitive to parameter variations and external disturbances.