Laser generated guided waves and finite element modeling for the thickness gauging of thin layers

Abstract

In this paper, nondestructive testing has been performed on a thin gold layer deposited on a 2 in. silicon wafer. Guided waves were generated and studied using a laser ultrasonic setup and a two-dimensional fast Fourier transform technique was employed to obtain the dispersion curves. A gold layer thickness of 1.33 microm has been determined with a +/-5% margin of error using the shape of the two first propagating modes, assuming for the substrate and the layer an uncertainty on the elastic parameters of +/-2.5%. A finite element model has been implemented to validate the data post-treatment and the experimental results. A good agreement between the numerical simulation, the analytical modeling and the experimentations has been observed. This method was considered suitable for thickness layer higher than 0.7 microm.

Characterization of micrometric and superficial residual stresses using high frequency surface acoustic waves generated by interdigital transducers

“…4,5 In recent years, several publications have demonstrated the relevance of this method for the characterization of thin films. [6][7][8] However, depending on the nature of the materials, the suitability of this method of generation varies according to the penetration depth and/or fragility of the layers (problem of ablation). Finally, the acoustic signature is also an interesting technique enabling measurements to be carried out at very high frequency.…”

Development of a Broadband (100–240 MHz) Surface Acoustic Wave Emitter Devoted to the Non-Destructive Characterization of Sub-Micrometric Thin Films

“…There are several methods used to obtain the phase velocity dispersion, and when considering the exploitation of the dispersion phenomena of the first Rayleigh mode, it is possible, for example, to apply a wavelet transform to signals corresponding to different propagation distances [ 30 , 31 , 32 ]. Phase velocities can also be obtained using a two-dimensional fast Fourier transform applied to time signals recorded at uniformly spaced intervals [ 33 , 34 ]. In this work, we decided to use a fast and efficient alternative method to estimate the velocities with a high accuracy.…”

Electrical and Optical Characterization of SAW Sensors Coated with Parylene C and Their Analysis Using the Coupling-of-Modes (COM) Theory

“…Several robust methods are applicable to measure SAW velocity accurately, for example, a wavelet transform [40] or a two-dimensional fast Fourier transform applied to signals recorded at uniformly spaced distances [41].…”