OBSERVATIONS OF PARTICLE LAYERS LEVITATED IN A RADIOFREQUENCY SPUTTERING PLASMA

Submicron carbon particles are grown in an argon radio-frequency (rf) sputtering plasma with graphite electrodes. In situ laser light scatte ring revealed particles levitated in the plasma in stratified layers, which were often thinner than 0.5 mm. Under some conditions, the numbe r of layers was very large. These layers are grouped into clouds. In a pure argon plasma, there is one cloud near the sheath edge above the lower electrode, while adding SF6 results in additional particle cloud s near the upper electrode and in the glow region. The different layer s appear to separate particles according to size, with the heaviest in the lowest layer. During several hours of plasma operation, the layer s collapsed and grew again into more stratified layers. The influence of parameters, such as gas pressure, rf power, electrode separation, a nd gas mixture was investigated. Scanning electron microscopy revealed that the particles were multisized spheres with a cauliflowerlike sur face. Some of the particles were found to be coagulated, due to collis ions within the plasma.