Epitaxial layers of the ternary alloy SiGeC were grown on [100] Si substrates. Using a rapid thermal chemical vapor deposition reactor working at low temperature and reduced pressure (550 degrees C and 1 Torr), we obtained SiGeC layers with a carbon concentration into substitutional sites of up to 1.5%. We used two methods to measure the substitutional C fraction in the SiGeC samples : Fourier transform infrared measurements at room temperature and x-ray diffraction of the d(004) atomic distance in the alloys. Using methylsilane (SiH3CH3, or MS) as the carbon precursor, we measured an activation energy for Si0.845Ge0.15C0.005 growth of around 52 kcal/mol and showed that C incorporation into substitutional sites saturates at high MS flows. Finally, thermal annealing of these ternary alloys has been studied : a 800 degrees C annealing for 15 min leads to oxygen and carbon diffusion, whereas strain relaxation occurs by amorphous SIC precipitation with a 900 degrees C, 15 min annealing.