Fundamental study of ion-irradiation effects on the columnar growth of chromium films prepared by ion-beam and vapor deposition

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The effects of ion irradiation during deposition on columnar growth of Cr thin films prepared by ion-beam-assisted deposition were studied. Cr films were prepared by evaporation of Cr metal and simultaneous irradiation of Ar ions onto Si 〈100〉 wafers. The energies of Ar ions were varied over the range of 0.5–20.0 keV, and the transport ratios of irradiating Ar ions to depositing Cr atoms, TR(Ar/Cr), to the substrates were also varied between 0.01 and 0.20. Vaporized Cr atoms were deposited onto substrates at an angle of 45° from the substrate normal and Ar ions were irradiated perpendicular to the substrate surface. Si substrates were not rotated and were kept at low temperature during deposition by a water-cooling system. The experimental results showed that every Cr film had a columnar structure regardless of ion-irradiation conditions. The column size became larger with increasing ion energy and TR(Ar/Cr). The growth direction of the column tilted considerably with increasing ion energy and TR(Ar/Cr) in the cases where the Ar-ion energy was 10.0 keV or less. On the other hand, the column growth direction became perpendicular to the substrate with increasing TR(Ar/Cr) in the case where the ion energy was 20.0 keV. The difference of column growth direction due to ion irradiation conditions could be understood by considering the preferential adatom movements as well as the shadowing effect.