Silicide-Formation-Induced Defects in Si Substrates in Ti/Si and Ni/Si Systems by a Monoenergetic Positron Beam

Abstract

The formation of silicides via the thin-film deposition of transition metals Ti and Ni onto Si substrates using a monoenergetic positron beam has been investigated. From the depth dependence of positron annihilation characteristics, the diffusion length of positrons was determined on the basis of a one-dimensional diffusion model. In the case of the Ti/Si system, the formation of the silicides did not induce shortening of the diffusion length of positrons in the Si substrate. On the contrary, the diffusion length of positrons in the resulting silicides was very short, indicating the presence of a great number of positron traps in silicides. The diffusion of Si atoms as a dominant diffusion species during TiSi2 formation could not be recognized in the present experiment. On the other hand, in the case of the Ni/Si system, the silicidation induced a very short diffusion length of positrons in the Si substrate. On the contrary, the diffusion length in the resulting silicide is long, to an extent comparable with that for defect-free metals. The diffusion of Si during NiSi2 formation was observed in the present experiment.