The kinetics of carbon sputter deposition on Si(100) substrates were studied by spectroscopic ellipsometry (SE) and X-ray reflectivity (XRR). The energy of ions bombarding the growing film varied by applying a bias voltage on the substrate inducing considerable changes of film density and composition. Both SE and XRR detected an initial nucleation stage during which a SiC interlayer was formed. A phenomenological model based on the rate equations for the carbon deposition on Si is proposed to describe the experimental results. The model includes the processes of carbon adsorption, formation of SiC and transition from sp(2) to sp(3) sites induced by low-energy ion bombardment. The calibration of the model was performed with the experimental results regarding the variation of deposition rates. It is shown that the non-monotonous kinetics of film growth is determined by the variations of surface composition at different stages of growth. The variation of model parameters, such as reaction constants and sticking coefficients, during fitting the experimental results for various ion energies extracted information regarding the prevailing processes taking place at each stage of the deposition process.