INNOVATIVE PLASMA DIAGNOSTICS AND CONTROL OF PROCESS IN REACTIVE LOW-TEMPERATURE PLASMAS

By means of two independent diagnostic methods, the plasma parameters in a RIE system (ALCATEL GIR 300) were measured. Density and collision rate of electrons and the power dissipated in the plasma body in He, Ar, O-2, CF4, and SF6 were determined. The first completely new diagno stic method is the self-excited electron plasma resonance spectroscopy (SEERS), which is based on the occurrence of harmonics in the dischar ge current due to the non-linearity of the sheath at the powered elect rode. Owing to the inductive behaviour of the plasma body (bulk, epsil on < 0) and the capacitive nature of the rf sheath, a non-linear and d amped series resonance can be observed and used for plasma diagnostics . Its eigenfrequency depends directly on the Langmuir frequency and th e electron density, respectively. In order to perform the measurement, the plasma monitoring system HERCULES, containing a robust numerical algorithm, was used. The second method is a completely automatic Langm uir probe (LP). The compensation of the rf signal was achieved by mean s of a triaxial setup. The measurement time of one I-V pair takes only 19.5 mu s. Retracting the probe tip pneumatically prevents undesirabl e coating. The I-V curve is smoothed by several FIR-filters to support the automatic calculation of the plasma parameters. Both methods have shown an agreement concerning the electron density and the possibilit y of advanced process control by innovative plasma diagnostics. (C) 19 98 Elsevier Science S.A.