The large lattice mismatch and different thermal dilatation make the pseudomorphic growth of 3C-SiC on Si to appear impossible. Therefore very thick films (greater than or equal to 20 mu m) have to be grown in order to relax the interface defects and obtain good quality heteroepitaxial films [H. Morkoc, S. Strite, G.B. Gao, M.E. Lin, B. Svertlov, M. Burns, J. Appl. Phys., 76 (1994 1363; S. Veprek, Th. Kunstmann, D. Volm, B. Meyer, J. Vac. Sci. Technol. A, 15 (1997) 10 (and references therein)]. In the course of the study of the initial stages of the growth using a UHV-compatible CVD apparatus and in-situ low energy electron diffraction (LEED) we find that up to several nm thin films provide LEED patterns corresponding to a 3 X 2 reconstructed surface las documented in literature for 3C-SiC surfaces) and appear relatively homogeneous. Increasing the thickness upon longer deposition time leads to the disappearance of this LEED pattern and to pronounced surface roughening. These results indicate that the novel organometallic CVD technique [Veprek et al.] may open a way towards the preparation of a pseudomorphic 3C-SiC films.