Fullerene ion (C 60+) damage in Si at 25°C

Abstract

A series of low-dose (< 5 × 10 12 ions cm −2) fullerene ion implantations in silicon has been carried out at 25°C over the energy range 100–530 keV. The resulting damage was measured quantitatively by Rutherford backscattering (RBS), using 2.0 MeV helium ions. This is an extension of an earlier study [J.B. Mitchell, J.A. Davies, L.M. Howe, R.S. Walker, K.B. Winterbon, G. Foti and J.A. Moore, Proc. 4th Intl. Conf. on Ion Implantation in Semiconductors, (Plenum Press, New York, 1975), p. 493.] of cluster-ion damage in Si where we had observed a 15-fold increase in damage-creation efficiency — i.e., the number of displaced Si atoms per keV of deposited energy — in going from (8.8 keV) monatomic carbon to (53 keV) C 6 +. Using the same 8.8 keV per carbon, we find that a 530 keV fullerene (C 60 +) ion displaces 100 times more Si atoms than a 53 keV C 6 + ion; thus C 60 + exhibits an additional 10-fold increase in damage creation efficiency compared to C 6 +. At 100 keV, the deposited (nuclear) energy density θ within the central core of each C 60 + cascade (∼ 1.5 ev per Si atom) is considerably larger than the Si heat of melting. Not surprisingly, the observed number of displaced Si atoms also exceeds the theoretical cascade volume, thus providing strong evidence for some sort of spike effect. Despite the high damage levels involved, scanning tunneling microscopy revealed no evidence of any anomalous surface structures or craters. Comparison of the present C 60 + data with earlier Si implantation studies, where a variety of ions (C, Ga, As, Sb, Te, Bi) and energies (10–60 keV) had been used, confirms the previous suggestion that room temperature damage in Si is governed mainly by the cascade energy density θ (eV/atom).