Using in situ reflection high energy electron diffraction (RHEED), ex situ atomic force microscopy (AFM) and transmission electron microscopy (TEM) the early stages of SiC growth on Si during the carbonisation were investigated in a solid source molecular beam epitaxy equipment. Different mechanisms of SiC precipitate growth by SSMBE were found. The SiC growth during carbonisation of Si(111) at 600 degreesC is controlled by diffusion and at higher temperatures by a two-dimensional nucleation process, which is mononuclear at 660 degreesC and polynuclear above 750 degreesC. At temperatures greater than 750 degreesC and 850 degreesC three-dimensional nucleation occurs at (111) and (100) surfaces, respectively.