CHARACTERIZATION OF PLASMA-SURFACE CONTACTS IN LOW-PRESSURE RF DISCHARGES USING ION ENERGY ANALYSIS AND LANGMUIR PROBES

The plasma-surface contact in low-pressure rf discharges in noble and reactive gases was studied by a combination of probe measurements and ion energy analysis at the surface. By comparing different methods, as the most reliable density determination the integral of the second de rivative of the probe curve was found. This method turned out to be no t very sensitive to incomplete rf filtering or compensation and even t o coating of the probe. However, it depends strongly on the correct ch oice of the plasma potential. By comparing space potentials obtained f rom probes and from ion energy distributions, a most probable value ca n be attained that is situated between the negative minimum and the cl osest maximum of the I''(U) curve. The ion energy distributions are co mpared to an analytical sheath model, giving very good agreement in an ab initio comparison. In plasmas depositing carbonized polymer films, reproducible structures due to the influence of the coating on the pr obe characteristics can be analyzed, yielding nonlinear I(U) character istics of the film. Using these characteristics, the film growth can b e followed.