レーザ周期加熱及び反射率温度測定法を用いたウェハ状固体試料の厚さ方向熱拡散率の光学的測定

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This paper presents a non-contact AC optical technique for measuring the thermal diffusivity of a wafer-like thin solid sample. The technique is based on heating one solid surface with a odulated laser beam and monitoring the corresponding temperature modulation of the other surface across the sample using the reflectance of a probe beam. The phase lag between the two laser signals is independent of the optical properties of the sample as well as the laser intensities, and can be related to the thermal diffusivity. A detailed theoretical analysis is presented to estimate the thermal diffusivity of the solid from the phase lag measured as a function of the modulation frequency. A closed form solution in the high-frequency limit is derived in order to provide a simple estimation procedure. The effect of misalignment of the two lasers is studied and conditions for making robust measurements are suggested. As a benchmark of this technique, the thermal conductivity of a single crystal silicon sample was measured to within 2 percent of reported values.
1999-09-25