Heat conduction in silicon thin films: Effect of microstructure
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Jason Xu and Andrew J. Steckl Nanoelectronics Laboratory, University of Cincinnati, Cincinnati, Ohio 45221 (Received 14 November 1994; accepted 21 April 1995)
A study was made of the thermal properties of low pressure chemical vapor deposition (LPCVD) silicon thin films with amorphous and polycrystalline microstructures, produced by varying the substrate temperature. Thermal diffusivity measurements were conducted using a thermal wave technique. The thermal diffusivity of the polycrystalline films was found to be about three times that of the amorphous films, but about one eighth that of bulk silicon single crystals. There was also an indication that the diffusivity increased with deposition temperature above the transition temperature from the amorphous to the polycrystalline state. The relationships between the thermal properties and micro structural features, such as grain size and grain boundary, are discussed.
I. INTRODUCTION Silicon is the most important material in semiconductor technology and microelectronics systems. Silicon thin films, both amorphous and crystalline, are of great practical importance in device design.1"3 In contrast to the extensive study of electronic, mechanical, and optical properties, little attention has been paid to the thermal properties of silicon films. Thermal properties of silicon films are potentially important not only for their scientific interest in relation to phonon scattering mechanisms, but also for practical reasons, as in advanced high-power devices. Because energy dissipation by local heating remains a critical limiting issue in device operation, 34 thermal conductivity of silicon films is a crucial performance and reliability factor in electronic circuits and integrated sensors. Existing thermal property studies have focused almost exclusively on bulk single-crystal silicon. However, thin films can have complex microstructures, 56 which can lead to thermal properties different from those of the bulk. 78 Such differences and the related microstructural origins have not been well studied for silicon. Measurement of thermal conductivities in thin film systems presents a special challenge to materials scientists and engineers. The major difficulty results from the very small thermal capacity of the film compared with that of the substrate, so that measurements tend to be insensitive to the presence of the film. With conventional contact probe techniques, 910 the accuracy is further compromised if the technique does not properly a) Guest
Scientist, on leave from Department of Physics and Astronomy, Wayne State University, Detroit, Michigan 48201. b) Guest Scientist, on leave from Department of Inorganic Materials Engineering, Seoul National University, Seoul, Korea. J. Mater. Res., Vol. 10, No. 8, Aug 1995 http://journals.cambridge.org
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account for the thermal contact resistance between the probe and the film. It is in this context that thermal wave techniques,11"14 with their noncontact configuration and capacity to probe local thermal proper
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