Sources and sinks of CF and CF2 in a cc-RF CF4-plasma under various conditions

In an asymmetric capacitively coupled radio-frequency (cc-RF) CF4 plasma, the radical densities of CF and CF2 were measured using laser-induced fluorescence spectroscopy. From the spatially (along the symmetry axis) and temporally (after switching off the discharge) resolved data, the source distribution and the sticking coefficients are inferred. We present results for three different electrode materials (stainless steel, aluminium and silicon). According to our data, the strength and the position of the sources depend strongly on the electrode material and the applied voltage. While the CF-sources are in the sheath in front of the powered electrode for stainless steel, they are on the surface of the powered electrode in the case of aluminium. By using a simple diffusion model for the analysis of the afterglow data, it can be shown that CF2 is destroyed exclusively at the walls and the decay time is determined by diffusion and sticking only. In contrast, for CF, surface as well as volume losses due to chemical reactions are important.