Effect of annealing on the elastic properties of copper thin films via laser ultrasonics

Abstract

The influence of rapid thermal annealing on the Young’s modulus of a copper (Cu) thin film was investigated using the laser-based surface acoustic wave spectrometry in the present study. Cu films with thicknesses ranging from 70 nm to 300 nm were prepared using a direct current magnetron sputter and heat-treated at 450 °C. The Young’s moduli of films were estimated from the analysis of the dispersive wave propagation behavior using the Transfer Matrix method. Results show that the modulus of as-deposited film increased by 21.5 % as the film thickness increased from 70 nm to 300 nm, attributed to abnormal grain growth. Upon annealing, it further increased to 124 GPa, accompanied by grain coarsening. X-ray diffraction analysis revealed dominant crystallite growth in the (111) orientation, suggesting that orientation-dependent microstructural evolution plays a key role in the modulus enhancement due to the elastic anisotropy of Cu.