We have investigated the structure and the growth mechanism of cubic silicon carbide (3C-SiC) films formed by thermal reaction of Si(111) and Si(100) substrates with C-60 molecules, using scanning tunneling microscopy (STM) and high-resolution transmission electron microscopy (HRTEM). The cross-sectional HRTEM images show the good epitaxial growth of SiC films on the Si(111) surface and the 3 x 3 surface reconstruction is observed by STM. In contrast, many dislocations are formed in the SiC films grown on the Si(100) surface and no surface structure is observed by STM. We find that the amorphous buffer layers, which have relevance to release the strain due to the lattice mismatching, are formed at the interface between SiC films and the Si(111) substrate.