INVESTIGATIONS ON PLASMA-ASSISTED SURFACE CLEANING OF ALUMINUM IN AN OXYGEN GLOW-DISCHARGE

Aluminum plates which are contaminated with hydrocarbon containing com pounds (oil, grease) were treated in an Ar-, O2- and Ar/O2-plasma gene rated by a dc-discharge. Besides a variation of the macroscopic discha rge parameters (power, pressure) also different modes (anomalous glow regime, hollow cathode regime) have been studied. In most cases the co ntaminated substrates served as cathodes of an anomalous glow discharg e where the combined influence of chemically reactive radicals and ene rgetic ions was very effective. During the plasma process the discharg e was monitored by means of power variation and optical emission spect roscopy. The spectral line intensities of several species (etchants an d products) have been measured as functions of the process duration. S imultaneously the removal of the contamination layers was observed by means of in-situ ellipsometry. The temporal change of the ellipsometri c parameters PSI and DELTA during the cleaning process was taken as a measure for the state of the surface. The combination of spectroscopic and ellipsometric measurements which indicate the progress of the pla sma treatment gave interesting results on the mechanisms at the surfac e. In addition. surface analysis was used to assess the quality of the substrates treated.