Cubic silicon carbide (3C-SiC) films were grown on Si substrates at 850 degrees C by sputtering of a pure-Si target in mixed Ar + CH4 discharges. Films were grown on Si(111), (001) and 4 degrees off-oriented (001) substrates. The effects of CH4 partial pressure (P-Ch4) on the film composition and microstructure were investigated using Auger electron spectroscopy, Rutherford backscattering analysis, X-ray diffraction and transmission electron microscopy. Epitaxial stoichiometric 3C-SiC films were obtained at P-CH4 = 0.6 mTorr. Lower methane partial pressure resulted in C-deficient films with a phase mixture of polycrystalline Si and amorphous SiC at P-CH4 = 0.4 mTorr. Increasing P-CH4 to 0.8 mTorr resulted in the growth of columnar SIC films with graphite precipitates at the grain boundaries. 3C-SiC epitaxial films deposited on Si(111) substrate showed a columnar structure from double-positioning domains. Films grown on Si(001) substrates resulted in smooth films, but with antiphase domain boundaries. The domain structure was removed when the films were grown on 4 degrees off-oriented Si(001).