Study of high reslution measurement of thin-film-thermal-properties by the ultra-high sensitive PAS

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Original point of our research is to evaluate thermal diffusivity of thin films deposited on the substrate. In the conventional PAS technique as the thermal diffusion length is much larger than the film thickness, it is impossible to evaluate the thermal property for the only films on the substrate. We proposed that the lateral thermal diffusion induced by the optical absorption can be detected by the tiny pyroelectric sensor.At first, we evaluated various bulk samples by the dimensional thermal propagation by the z-cut LiNbO3 pyroelectric element and found that those thermal diffusivities are Si : 0.87, Cu : 0.96, InP : 0.44, GaAs : 0.25, Ta : 0.24 [cm2/s]. Those values are within 5% difference compared with handbook data.Next, we evaluated a-1 mu m-thick Si thin film deposited on the quartz substrate. We assumed that when laser beam is irradiated on the film thermal resistance is assumed a parallel connection with the resistance of film and that of substrate. It is easy to separate those two resistances experimentally. Thus, We established how to measure the thermal diffusivity and found that the value for quartz substrate is 7.18*10^3 [cm^2/s] and that for Si thin film is 0.65 [cm^2/s].