A novel way to quantitatively determine the mechanical properties of thin films from the initial-grown surface by nanoindentation

Abstract

A novel way was derived in this work to quantitatively determine the mechanical properties of thin films grown on silicon substrates from the initial-grown surface using nanoindentation. The as-deposited surface of the films was firstly glued to steel and subsequently, the silicon substrate was etched away in a hot potassium hydroxide (KOH) solution. Steel served as supporting material after the removal of the substrate. This procedure enables the exposure of the initial-grown surface of the film with a surface roughness close to the one of the silicon substrate (around 1 nm), which typically is significantly lower than the as-deposited surface (usually 20 to 30 nm). Carrying out indents on the initial-grown side allows us to acquire reliable results by avoiding any artifact due to surface roughness. Measurements were performed on nanocrystalline SiC and diamond films to confirm the validity of this method. Finally, a 13 μm thick diamond/SiC composite film composed of nanocrystalline SiC and nanocrystalline diamond was prepared and characterized by applying this method. The composite film exhibits a hardness of 49.8 ± 2.1 GPa, an elastic modulus of 598 ± 25 GPa, which is directly comparable to the value gained by the surface acoustic wave (SAW) method. Moreover, the hardness and elastic modulus of the composite film both accord well with the values predicted from the mechanical properties of the individual phases. Therefore, mechanical property determination from initial-grown surface is a promising approach for a variety of hard brittle thin film systems with high surface roughness.