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

Aluminum plates which are contaminated with hydrocarbon containing compounds (oil, grease) were treated in an Ar-, O2- and Ar/O2-plasma generated by a dc-discharge. Besides a variation of the macroscopic discharge parameters (power, pressure) also different modes (anomalous glow regime, hollow cathode regime) have been studied. In most cases the contaminated substrates served as cathodes of an anomalous glow discharge where the combined influence of chemically reactive radicals and energetic ions was very effective. During the plasma process the discharge was monitored by means of power variation and optical emission spectroscopy. The spectral line intensities of several species (etchants and products) have been measured as functions of the process duration. Simultaneously the removal of the contamination layers was observed by means of in-situ ellipsometry. The temporal change of the ellipsometric 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 plasma treatment gave interesting results on the mechanisms at the surface. In addition. surface analysis was used to assess the quality of the substrates treated.