Nanoindentation behaviour and microstructural evolution of Au/Cr/Si thin films

Abstract

The nano-mechanical properties of an as-deposited composite Au/Cr/Si film comprising a Au layer with a thickness of 800 nm and a Cr adhesive layer with a thickness of 10 nm deposited on a Si (100) substrate are investigated by performing nanoindentation tests to a maximum depth of 1500 nm. The microstructural evolutions of as-deposited indented specimens and specimens annealed at temperatures of 523 K, 623 K or 723 K for 2 min are then examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The loading curve for the as-deposited Au/Cr/Si thin film is found to be continuous and smooth. However, the unloading curve has a prominent pop-out feature. The hardness and Young's modulus of the Au/Cr/Si thin film indented to a maximum depth of 1500nm are determined to be 2.7 GPa and 110 GPa, respectively. In the as-deposited sample, the microstructure of the indentation zone is characterised by a mixed structure comprising amorphous phase and nanocrystalline phase. Furthermore, well-defined Au, Cr and Si layers are observed in the interfacial region of die thin film. However, at the highest annealing temperature of 723 K, the microstructure of the indentation zone is recovered to a perfect diamond cubic single crystalline state. Finally, silicidation of the Cr layer takes place in all the annealed samples, resulting in the formation of isolated nano-islands of Cr. ©2009 The Thermoelectrics Society of Japan.