Particulate growth in a 13.56 MHz radiofrequency methane plasma: influence of the flow rate and the incident rf power

Abstract

The generation and the behavior of amorphous hydrogenated carbon particulates in a pure methane rf discharge have been studied for different methane flow rates (2−14 sccm) and different incident rf powers (40−120 W). Laser light scattering provides informations on their localization in the discharge. The 90° laser light scattered is used to determine the appearance times. The higher the incident rf power, the shorter the particulate appearance time: conversely the higher the methane flow rate, the higher the appearance time. The appearance times have been correlated to the inverse of the residence times of CH 4 molecules. Good correlations have been observed between the particulate generation and the time evolutions of both laser beam extinction and dc self bias voltage. Whatever our experimental conditions, the influence of the methane flow rate seems lower than the rf power one. An increase of the rf power leads to a more important generation of particulates in the plasma.