[en] Silicon carbide (SiC) films were grown on Si(111) substrates by low-energy ion beam deposition for the purpose of investigating momentum effects on crystal growth. Dimethylsilane (SiH₂(CH₃)₂) was ionized to obtain methylsilicenium ions (SiCH₃⁺) with Si-C bonding for use as precursors. The ion beam was extracted at 25 m keV for efficient transport from the ion source to the deposition chamber, and SiCH₃⁺ ions were mass-selected by a sector magnet. Ions transported at high energy were decelerated in front of the substrate to desired energies of 20-100 eV. Ion beam current at the substrate was 0.1-0.2 μA. Temperature at the Si(111) substrate was held at 750 deg. C during ion beam deposition and pressure in the deposition chamber atmosphere was kept below 3.9x10^-7 Pa. Incident SiCH₃⁺ ions measured with an energy analyzer were found to have monochromatic energy distributions, e.g. the FWHM was only 1 eV in the case of 100 eV. Crystal structures of the SiC thin films were analyzed in situ by reflection high-energy electron diffraction (RHEED). Under conditions of incident SiCH₃⁺ ions energies of 60-100 eV, 3C-SiC(111) was grown on Si(111) substrate. On the other hand, under conditions of incident ion energies of 20-50 eV, 2H-SiC was grown on Si(111) substrate. In conclusion, the momentum of low-energy ions was found to exert an effect on the determination of SiC crystal structures