Surface Acoustic Wave Methods to Determine the Anisotropic Elastic Properties of Thin Films

Published

September 1, 2001

Author(s)

Donna C. Hurley, Vinod K. Tewary, A J. Richards

Abstract

We have developed laser ultrasonic methods to measure the elastic properties of thin films. In this approach, surface acoustic waves (SAWs) were generated using a line-cocused laser with a pulse width of 0.2 ns. Waves with frequency components up to 400 MHz were detected by a line- or point-focused Michelson interferometer with a 3 dB bandwidth of 800 MHz. Dispersion relations for the SAW phase velocity were calculated from several displacement waveforms acquired with source-detector separations between 5 and 15 mm. To determine the elastic properties of the films, we applied to our data an inversion algorithm based on the delta-function representation of the elastodynamic Green's function. Two different film-substrate systems were used to demonstrate the validity of our methods: an elastically isotropic aluminium film on an isotropic fused silica substrate and an isotropic molybdenum film on an anisotropic, single-crystal silicon wafer. The values for Young's modulus and Poisson's ratio fo the films as determined by our methods were in good agreement with literature values for these materials in bulk form. Results from these samples are also used to discuss aspects of measurement uncertainty.

Citation

Measurement Science & Technology

Volume

12

Issue

No. 9

Pub Type

Journals

Keywords

elastic moduli, laser ultrasonics, surface acoustic waves, thin films

Citation

Hurley, D. , Tewary, V. and Richards, A. (2001), Surface Acoustic Wave Methods to Determine the Anisotropic Elastic Properties of Thin Films, Measurement Science & Technology (Accessed April 25, 2024)