Nanoindentation Behaviour and Annealed Microstructural Evolution of Ni/Si Thin Film

摘要

The nano-mechanical properties of as-deposited Ni/Si thin films indented to a maximum depth of 800 nm are measured using a nanoindentation technique. The microstructural evolutions of the indented as-deposited specimens and indented specimens annealed at 200°C, 300°C, 500°C and 800°C for 2min, respectively, are examined via transmission electron microscopy (TEM) and micro-Raman scattering spectroscopy (RSS). The loading curve for the as-deposited Ni/Si thin film is found to be continuous. However, the unloading curve has a prominent pop-out feature. The hardness and Young's modulus of the Ni/Si thin film are found to vary with the nanoindentation depth, and have values of 13 GPa and 177 GPa, respectively, at the maximum depth of 800 nm. The deformation induced in the nanoindentation process causes the microstructure of the indented zone in the as-deposited thin film to transform from a diamond cubic structure to a mixed structure comprising both amorphous phase and metastable Si 111 and Si XII phases. However, after annealing at temperatures of 200°C~500°C and 800°C, the microstructure within the indented zone contains only Si III and Si XII phases and epitaxial NiSi_2 phase, respectively. The annealing process prompts the formation of nickel silicides at the Ni/Si interface. The silicides have the form of Ni_2Si in the samples annealed at 200°C, but transform to low-resistivity NiSi at annealing temperatures of 300°C or 500°C. At the highest annealing temperature of 800°C, the NiSi phases are replaced by high-resistivity NiSi_2 phases.