Laser Induced Stress Wave Thermometry for In-situ Temperature and Thickness Characterization of Single Crystalline Silicon Wafer: Part I-Theory and Apparatus
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abstract
The feasibility of Thermo-Acousto-Photonic Nondestructive Evaluation (TAP-NDE) as an alternative to current pyrometric and ellipsometric techniques to simultaneously measure temperature and thickness during single crystalline silicon wafer processing is investigated. TAP-NDE is a non-contact, non-invasive, laser-based ultrasound technique employed to profile the thermal and spatial characteristics of the wafer using Lamb waveguide modes. A theoretical formulation viable for identifying the frequencies sensitive to temperature and thickness changes is presented. The group velocity of the frequency components and their corresponding changes with respect to temperature for different thicknesses are modeled by considering a titanium bonding layer between aluminum/copper and silicon. It is shown both theoretically and experimentally that there exists a correlation for differentiating thickness variation as a function of varying group velocities for different frequencies at different temperatures, thus establishing the groundwork for the optically generated Lamb wave thermometric methodology for silicon wafer. 2010 Society for Experimental Mechanics.
