Oxygen impurity effects at metal/silicide interfaces: Formation of silicon oxide and suboxides in the Ni/Si system

Abstract

The effect of oxygen impurities on the Ni/Ni2Si interface has been investigated via ion implantation using x-ray photoelectron spectroscopy (XPS), 4He + backscattering, and 16O(d,alpha)14N nuclear reactions. Oxygen dosages corresponding to peak concentrations of 1, 2, and 3 atomic percent were implanted into Ni films evaporated on Si (100) substrates. The oxygen, nickel, and silicon core lines were monitored as a function of time during in situ growth of the Ni silicide to determine the chemical nature of the diffusion barrier known to form in the presence of oxygen impurities. It is shown that neither Ni oxide or mixed compounds such as Ni2SiO4 are involved in the barrier formation. The data demonstrate that as the advancing Ni/Ni2Si interface encounters oxygen in the Ni film, silicon suboxides (Si2O3, Si2O, and SiO) are formed. As more oxygen is encountered, Si takes on a full coordination of oxygen, forming SiO2. When a sufficient layer of SiO2 has formed, Ni metal is no longer able to diffuse through to the Si/Ni2Si interface to continue the solid phase reaction. It has been determined under UHV annealing conditions that the amount of oxygen necessary to stop the Ni diffusion is 2.2×10^16 O/cm^2. These experiments also provide a novel approach for synthesizing Si oxides and suboxides in a metallic matrix for examining relaxation effects in XPS as well as providing model compounds for Si/SiO2 interfacial studies.

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