Analysis of thermal parameters and factors acting on thermal conduction of low-k films

The thermal properties of a silicon oxide-based low-k film and a thermally oxidized silicon film were investigated using the 3-omega and laser thermo-reflectance (LTR) methods. Thermal conductivity and effusivity were successfully estimated by the 3-omega and LTR methods, respectively. It was confirmed that the combination of thermal effusivity and conductivity can successfully provide the heat capacity and thermal diffusivity of the films. The thermal parameters thus obtained suggested that the lower thermal conductivity of the examined low-k film comes mainly from the rather low level of thermal diffusivity. Based on an analysis of the X-ray diffraction profiles of the films, it was found that the low thermal diffusivity of the low-k film can be attributed to the discontinuity of the network structure of their clusters. The heat resistance at the interface between the film and Si substrate was also evaluated. We found that the low-k film exhibited, interestingly, negative interfacial heat resistance, although interfacial heat resistance should have a positive value in general. In order to determine the origin of the negative interfacial heat resistance, the interface state of the films was analyzed in detail on the basis of X-ray reflectivity (XRR) measurements. The XRR results showed clearly that a thin, high-density layer was present at the interface of the low-k films. This high-density layer presumably promoted heat flow to the substrate, resulting in the apparent negative interfacial heat resistance.