We studied the interaction of elemental carbon with Si(111) and Si(100) surfaces with in situ real time spectroscopic ellipsometry at different C exposures ranging from 7 x 10(12)-7 x 10(14) cm(-2) s(-1) at 750 degrees C under UHV conditions in a molecular beam epitaxy equipment. The optical investigations were accompanied by real time RHEED studies. Using an optical three layer model (surface roughness, SiC layer, interface) on Si substrate the ellipsometric response allowed us to determine and quantify the different stages of the process: the nucleation, the coalescence, the growth kinetics, and the surface and interface evolution. The SiC film growth depends on C exposure and weakly on substrate orientation. The results obtained were compared to the RHEED observations.