IR-SPECTRA RESOLUTION IN FLUORINATED SILICON-NITRIDE FILMS

The broad i.r. Si-N band (700-1200 cm-1) in fluorinated silicon nitride films has been resolved. I.r. spectra of the samples have been fitted using Gaussian curves centred in positions determined from the maxima of the negative second derivative of the digitized spectra. In silicon nitride films deposited by plasma-assisted chemical vapour deposition from SiH4-NF3-NH3-N2 gas mixtures, -SiF(n) radicals (n = 1-3) incorporated in their structures have been detected. The relative concentrations of the different fluorine radicals present in the network depend on the NF3 flow ratio used. As the flow ratio increases above 0.5, -SiF and -SiF2 concentrations in the film reach the steady state. However, an appreciable increase in -SiF3 and [-SiF2-]n concentrations has been observed.