Abstract
The silicide phase formation is examined in the Ni/Si system. The multiphase of NiSi and NiSi2 is confirmed in the specimen, in which a 30-nm-thick Ni film is sputter-deposited on Si(100) at 350°C and subsequently annealed at 400°C for 1 h. This is interpreted that the NiSi and NiSi2 phases nucleate from the amorphous alloys, as a super-cooled melt, at the composition corresponding to those of eutectic points in different composition, which appear in the intermixed Ni-Si alloy layer with a Ni concentration gradient owing to intermixing between Ni and Si at the interface. To confirm this consideration, we execute the Ni deposition on a 350°C-heated Si substrate with a thin SiO2 layer. The result indicates the direct formation of NiSi2 in a non-uniform fashion. This is because the thin SiO2 layer suppresses the Ni diffusion into Si, resulting in the formation of a Ni-Si alloy in a Si-rich composition, from which NiSi2 nucleates at a low temperature. We can demonstrate that the high-temperature phase of NiSi2 nucleates by the kinetic constraint from the amorphous alloy of suitable composition.
