IN-SITU INFRARED-ABSORPTION SPECTROSCOPY OF DUSTY PLASMAS

II? situ, time-resolved Fourier transform infrared spectroscopy was us ed to study particulate formation in rf discharges in mixtures of sila ne, argon, and nitrogen. The spectra were taken at a maximum rate of 2 0 Hz. The discharge conditions were chosen such that previous calibrat ions of the time evolutions of particle size and density could be used . The measurements indicate that the onset of the solid-state vibratio nal absorptions of the SIH and SiH2 bands only takes place after the n ucleation and coagulation phase have finished; it coincides with the p reviously predicted start of the deposition of amorphous hydrogenated silicon on the particles. The dissociation of the silane feed gas is f ound to be in the range of 30%, and its time development suggests that also the large-scale dissociation of silane only starts after the coa gulation phase. This is in agreement with previously observed trends f or the electron temperature. If silicon partilces are grown in the pla sma, and the silane flow is stopped, the Si particles stay trapped in the glow. The infrared measurements, however, show that they almost co mpletely oxidize: the SiH/SiH2 vibrations disappear and a strong SiO v ibration appears. If nitrogen gas is allowed into the plasma, the SiO vibration is replaced by a SiN vibration. (C) 1996 American Vacuum Soc iety.