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Formation of nickel-platinum silicides on a silicon substrate: Structure, phase stability, and diffusion from ab initio computations

Mikael Christensen, Volker Eyert, Clive M Freeman, Erich Wimmer, A Jain, J Blatchford, D Riley, and J Shaw
Journal of Applied Physics 114, no. 3: 033533. (2013)
doi: 
10.1063/1.4816094

The formation of Ni(Pt)silicides on a Si(001) surface is investigated using an ab initio approach. After deposition of a Ni overlayer alloyed with Pt, the calculations reveal fast diffusion of Ni atoms into the Si lattice, which leads initially to the formation of Ni₂Si. At the same time, Si atoms are found to diffuse into the metallic overlayer. The transformation of Ni₂Si into NiSi is likely to proceed via a vacancy-assisted diffusion mechanism. Silicon atoms are the main diffusing species in this transformation, migrating from the Si substrate through the growing NiSi layer into the Ni₂Si. Pt atoms have a low solubility in Ni₂Si and prefer Si- sites in the NiSi lattice, thereby stabilizing the NiSi phase. The diffusivity of Pt is lower than that of Ni. Furthermore, Pt atoms have a tendency to segregate to interfaces, thereby acting as diffusion barriers.