Redistribution of phosphorus during Ni_0.9Pt_0.1-based silicide formation on phosphorus implanted Si substrates

Phosphorus diffusion and its distribution during the solid-state reactions between Ni_0.9Pt_0.1 and implanted Si substrates are studied. Silicidation is achieved through a first rapid thermal annealing followed by a selective etching and a direct surface annealing. The redistribution of phosphorus in silicide layers is investigated after the first annealing for different temperatures and after the second annealing. Phosphorus concentration profiles obtained thanks to time of flight secondary ion mass spectrometry and atom probe tomography characterizations for partial and total reactions of the deposited 7 nm thick Ni_0.9Pt_0.1 film are presented. Phosphorus segregation is observed at the Ni_0.9Pt_0.1 surface and at Ni₂Si interfaces during Ni₂Si formation and at the NiSi surface and the NiSi/Si interface after NiSi formation. The phosphorus is evidenced in low concentrations in the Ni₂Si and NiSi layers. Once NiSi is formed, a bump in the phosphorus concentration is highlighted in the NiSi layer before the NiSi/Si interface. Based on these profiles, a model for the phosphorus redistribution is proposed to match this bump to the former Ni₂Si/Si interface. It also aims to bind the phosphorus segregation and its low concentration in different silicides to a low solubility of phosphorus in Ni₂Si and in NiSi and a fast diffusion of phosphorus at their grain boundaries. This model is also substantiated by a simulation using a finite difference method in one dimension.