Mesure de la conductivité thermique de matériaux en films minces par la méthode 3-oméga et caractérisation des résistances thermiques interfaciales substrat/film.

Abstract

The deposition of materials in thin layers arouses a great interest in the industrial and academic sectors of various fields such as for example micro and nanoelectronics. In this context, knowledge of the thermal properties of thin film materials, and in particular of thermal conductivity, is essential for optimizing the performance of many devices. Nevertheless, the measurement of these parameters remains difficult given the small dimensions involved. In particular, the existence of an interfacial thermal resistance on the one hand between the deposited layer and the host material and on the other hand between the thin layer and temperature sensor makes the rigorous extraction of thermal conductivity delicate. Among the measurement methods likely to respond to this problem, our choice fell on the 3-omega (3ω) differential technique, which was introduced by DG Cahill, because of its simplicity of use, its precision and low heat loss by thermal radiation caused during the measurement. This method requires the deposition, by optical photolithography, of a metal line deposited on the surface of the sample to be characterized. The line acts simultaneously as a heating element and a temperature sensor. It is then necessary to acquire the voltage of the 3rd harmonic (V_3ω: hence the name of the method) to go back to thermal conductivity. This measurement is done using a dedicated measurement bench developed in the laboratory. This experimental work is accompanied by modeling studies using the formalism proposed by DG Cahill and also by a Finite Element Approach (FEM) using the Comsol Multiphysics software, to estimate thermal conductivity and interfacial thermal resistance. Between the different materials constituting the sample (heating element / film, film / substrate). The comparison of the experimental results with those resulting from the analytical model of D. G. Cahill and numerical simulations by FEM shows that we have two efficient complementary tools for the determination of the thermal conductivity of materials in thin layers and the interfacial resistance. Besides these two tools, the existence of a reliable measuring device makes it possible to note the expertise acquired in the determination of the thermal conductivity of solid materials or thin films.