Hydrofluorinated amorphous silicon–carbon alloys(a-Si1−xCx:H,F)are obtained by plasma decomposition ofSiF4–CH4–H2mixtures. The analysis of the plasma phase, by mass spectrometry and optical emission spectroscopy, and of the resultant material, by Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy, allows us to gain information about the film growth chemistry. The growth kinetics and the material composition of thea-Si1−xCx:H,Ffilms are studied as a function of the addedCH4amount to theSiF4.The peculiarity ofSiF4–CH4system is that smallCH4addition (10%) toSiF4produces silicon carbon alloys with high C incorporation (60 at. %). This has been explained on the basis of a growth model in which the chemisorption ofCHnon the surface prevails on that ofSiFn.