Diamond deposition on an epitaxial CoSi2 layer over Si(111) is preceded by the formation of a 4 nm thick silicon carbide layer. The steps of carbide formation, diamond nucleation and diamond growth are monitored in situ by three electron spectroscopies (x-ray photoelectron spectroscopy, Auger electron spectroscopy, and electron-loss spectroscopy). By comparison with our previous studies of diamond growth on clean Si(100) and Si(111), the time required to stabilize the SiC composition is much longer. This slow step is interpreted by a strong carbon diffusion into the bulk which goes together with silicon enrichment of the carbide phase. The lack of carbon saturation at the surface induces a large delay for the subsequent diamond nucleation process by a time scale factor of 10. In addition, the electron spectroscopy measurements reveal the appearance of C-C sp(3) species before the diamond nucleation starts. These species probably correspond to carbon aggregates which act as precursors of the diamond phase,