Fluorocarbon (CFx+), fluorine and carbon (C+) ion beams with high current density (50 < J(i) < 800 mu A/cm(2)) were irradiated to Si and SiO2 surfaces to investigate the influence of the ion species on he etching efficience. the ion beams were extracted from magnetized helicon-wave CF4 plasmas operated in pulsed modes. The CF3+ beam had the largest etching efficiency for Si at the same beam energy. When the same data were summarized as a function of the momentum of the incident ion beam, the difference in the etching efficiency became small, although the CF3+ beam still had a slightly larger etching efficiency. On the other hand, the etching efficiency for SiO2 by the CF3+ beam was larger than that by the other ion beams in the low-momentum region. In addition, in the low-momentum region, the etching efficiency for SiO2 by CF3+ with SiO2, leading to the high etching selectivity of SiO2 over underlying Si in the fabrication of semiconductor devices.