Development of a Surface Acoustic Wave Measurement System Using Laser-ultrasound and Its Application to Elastic Property Evaluation of Thin-films

A measurement system was established to evaluate Young's modulus of thin films using the propagation behavior of the laser-induced surface acoustic wave (SAW). A nanosecond-laser beam was focused onto the surface of the thin film to generate SAW at the locally heated spot, and its time-domain waveforms were obtained using a laser interferometer by measuring the surface displacement. The transfer matrix method was used to calculate the dispersion curve such that Young's modulus of the film can be deduced from the experimental data by curve-fitting. A 1.0 mu m-thick titanium (Ti) film was tested, and the results were in good agreement with that of the nanoindentation testing with an error percentage of 6.3%. In addition, 240 nm Ti was tested, and only a 2.7% increase in the elastic property was observed, showing that the scale effect is not significant.