Young's modulus determination of soft metal thin films by nanoindentation technique based on the constant modulus assumption analysis

Nanoindentation tests were performed on the copper film with thickness of 400 nm deposited on the silicon (100) wafer by plasma-assisted deposition technique, which were annealed in vacuum at 300°C. The methods of determining the Young's modulus of film-only applicable for the soft metal thin films on hard substrate were investigated. The results show that the calculation method based on the constant modulus assumption can effectively avoid the strong influence of materials pile-up and substrate minimization on the evaluated results in the Oliver-Pharr analysis. Combined with the continuous stiffness measurement (CSM) technique, the error influence factors of material creeps and thermal drift in the Oliver-Pharr analysis are eliminated. The Young's modulus of copper films determined by this way is 92.2 ± 1.8 GPa, which is consistent well with literature. Compared with the common methods that the intrinsic modulus of thin films needs to be separated from the composite modulus via the mathematic models, the present method is more accurate and simple.