Enhanced Diffusion and Lattice Location of Indium and Gallium Implanted in Silicon

Indium and gallium were implanted into silicon at 45 keV to a dose of ∼10 15 ions/cm 2 and concentration profiles were determined by neutron activation analysis in a study of enhanced diffusion of the implanted species. Indium and gallium showed enhanced diffusion at implant temperatures from ∼250°C to 700°C (In) and ∼150°C to 700°C (Ga), the effect being independent of both temperature and dose rate over these temperature ranges. On the basis of 1 MeV helium backscattering measurements it is concluded that, for 700°C implants, almost 100% of the indium atoms and 75% of the gallium atoms in the deeply penetrating tails, i.e. beyond 650Å, were located on nonlattice sites. In the case of the 300°C Ga implant, about 50% of the atoms in the tail of the distribution were found on non-lattice sites; however, very few (<10%) were in the tetrahedral interstitial position. An interstitial diffusion mechanism is proposed. Backscattering measurements also revealed that the silicon disorder remaining in the crystal after implantation of either In or Ga decreased monotonically with increasing implantation temperature up to 500°C. For implantations at or above 500°C, a "disorder" signal was observed from deeper within the crystal and the dechanneled fraction of the beam increased.