FULLERENE ION (C-60(-DEGREES-C()) DAMAGE IN SI AT 25)

A series of low-dose(<5 X 10(12) ions cm(-2)) fullerene ion implantati ons in silicon has been carried out at 25 degrees C over the energy ra nge 100-530 keV. The resulting damage was measured quantitatively by R utherford 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. C onf. on Ion Implantation in Semiconductors, (Plenum Press, New York, 1 975), 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 disp laced Si atoms per keV of deposited energy - in going from (8.8 keV) m onatomic 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 mo re Si atoms than a 53 keV C-6(+) ion; thus C-60(+) exhibits an additio nal 10-fold increase in damage creation efficiency compared to C-6(+). At 100 keV, the deposited (nuclear) energy density theta within the c entral core of each C-60(+) cascade (similar to 1.5 ev per Si atom) is considerably larger than the Si heat of melting. Not surprisingly, th e observed number of displaced Si atoms also exceeds the theoretical c ascade volume, thus providing strong evidence for some sort of spike e ffect. Despite the high damage levels involved, scanning tunneling mic roscopy revealed no evidence of any anomalous surface structures or cr aters. Comparison of the present C-60(+) data with earlier Si implanta tion studies, where a variety of ions (C, Ga, As, Sb, Te, Pi) and ener gies (10-60 keV) had been used, confirms the previous suggestion that room temperature damage in Si is governed mainly by the cascade energy density theta (eV/atom).