Ultrasonic Time-Frequency Characterization of Silicon Wafers at Elevated Temperatures

A methodology to characterize and quantify the thermo-mechanical properties of silicon wafers is presented. The method applies broadband Thermo-Acousto-Photonic (TAP) NDE techniques to both generate and detect analyzing guided Lamb waves in wafer structures. Optically induced, dispersive acoustic waves carry important information pertaining to the variation of mechanical properties due to temperature changes. To quantify the variation as functions of temperature, a spline-wavelet based fast integral wavelet transform is employed to identify the temporal progression of the multi-modal structure of dispersive waveguide modes. These results are then used to extract group velocities of particular frequency components of interest. Examples are given to demonstrate the effectiveness of the method on experimental data acquired using the Fiber Tip Interferometer (FTI) system developed at Texas A&M University.