Proceedings PaperThickness measurement on multilayered structures by SAW dispersion
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The characterization of layered media, for example in semiconductor technology, can be one important field for future application of acoustic microscopy. Opaque layers can be evaluated in a nondestructive way without the need of edges. The measurements require pads of 40 $CCL 40 micrometers 2. This leads to a spatial resolution of the same magnitude. For further applications it seemed to be of technological interest to expand this method on buried layers. Thickness measurements are based on the comparison of surface acoustic wave (SAW) speed evaluated using the V(z)-option of the acoustic microscope with theoretically predicted values. We used a mathematical model for the description of sound propagation in multilayered structures by Thomson and Haskell to calculate the SAW-speeds for a given system of layers. The evaluation of SAW-speed from measured V(z)-curves with high accuracy was performed by means of FFT-algorithm. By comparing calculated SAW-speed values with results from measurement it was possible to verify the theoretical approach.