Lateral Extensions to Nanowires for Controlling Nickel Silicidation Kinetics: Improving Contact Uniformity of Nanoelectronic Devices

Although widely applied as contacts to nanoelectronic devices, metal silicides in nanostructures suffer from varying compositions and growth rates. To study the underlying kinetics and to control the reactions, we introduce local volume extensions (“polders”) to silicon nanowires. This method allows to decouple the silicide growth process from variations in the metal supply and to gain a reduced length growth rate as long as the silicon reaction volume is available in the polders. In situ analyses are performed by scanning electron microscopy during the anneal to extract the growth rates. A deterministic limitation of silicide growth by nickel flux, NiSi2 reaction rate, and nickel diffusion is observed. The extracted maximal reaction rate at the NiSi2–Si interface allows to determine the activation energy. Subsequent transmission electron microscopy reveals an epitaxial {111} NiSi2–Si interface in the ⟨011⟩-oriented nanowire. It is also seen that the polders suppress Ni-rich silicide phases and give rise to the formation of a single-crystalline Ni–Si phase with a Ni/Si ratio close to 1:1. Retarded growth by the application of polders can almost stop the silicidation in nanowires at a defined point even for different Ni fluxes. This can help to reduce gate overlap and channel length variation, especially in Schottky-junction-based field-effect transistors. Geometric optimization of the polder regions with regard to the largest impact is discussed.