Solid state reactions and diffusion processes in metal - Si 3N 4 - Si thin film systems—a comparison between Cr, Co and Ni metals

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Solid state interfacial reactions between thin metal films of Cr, Co and Ni and LPCVD Si 3N 4 films have been investigated over the temperature range from 400 to 1200°C. The composition, structure and distribution of the reaction products were analysed by TEM, SEM, X-ray diffraction and Auger electron spectroscopy. Cr, Co and Ni metals were chosen for the comparison because of their different chemical reactivities with Si and nitrogen. In the case of the Co, Ni/Si 3N 4/Si systems, the formation of metal silicides was influenced by the counter-directional diffusion of the metal and Si through the Si 3N 4 layer. As a result, an island-like structure of metal silicides was obtained on both sides of the Si 3N 4 film. In the case of Cr/Si 3N 4/Si, the Cr reduced the silicon nitride above 900°C to produce a multiphase structure of chromium silicide and nitride. Thermodynamic considerations based on published phase diagrams were used to explain the experimental results.