Ar RF discharge. Strong absorption bands at 1000-1100 cm-1 have been found and attributed to C-F and Si-F absorption. Furthermore continuous extinction due to Rayleigh and Mie scattering has been observed. The relative intensities of C-F, Si-F and scattering signals vary with plasma conditions. There are several experimental indications that the clusters are formed on the surface and ejected into the plasma. An SEM study of the substrate surface has allowed us to establish the mechanism for the particulate production in this discharge.