Resonance Ultrasound Spectroscopy for Measuring Elastic Constants of Thin Films

概要

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We show an advanced technique for measuring elastic constants $C_{ij}$ of thin films deposited on substrates. Thin films often show anisotropy between the in-plane and out-of-plane directions because of their columnar structure, residual stress, texture, and incohesive bond. Then, thin films show macroscopically transverse isotropy and have five independent $C_{ij}$. All the film $C_{ij}$ affect free-vibration resonance frequencies of the film/substrate layered specimen. Therefore, measuring the resonance frequencies permits us to determine the thin-film $C_{ij}$ with the other known parameters. In order to yield reliable $C_{ij}$ of thin films, we have to measure the resonance frequencies with sufficient accuracy and identify vibration modes of the measured resonance frequencies. We overcome these problems by developing a tripod and using a laser-Doppler interferometer, respectively. We applied the present technique to a copper thin film. Measured $C_{ij}$ are smaller than those of bulk and show elastic anisotropy. We attribute these features to the incohesive bond regions.
2004-05-15