Thermal conductivity of low-k films of varying porosity and direct measurements on silicon substrate

We have studied the thermal conductivity of a variety of low-dielectric constant (low-k) materials with differing porosities by a nanosecond thermoreflectance measurement system (Nano-TheMS). The Nano-TheMS utilizes thermoreflectance to probe the thermal conductivity of nanometer-order thin films. The porosity of low-k materials is one of most significant factors in determining the dielectric constant and mechanical strength of low-k films. The temperature dependence of the thermal conductivity was measured for four low-k films with differing porosities for temperatures up to 300 °C. The thermal conductivity was found to decrease with increasing porosity and the temperature dependence was slight. The Nano-TheMS has been upgraded to allow for direct measurement of low-k film grown on silicon substrate by switching from a front-detection-rear-heating (FR) to a front-detection-front-heating (FF) pump/probe arrangement. The values of the thermal conductivity for low-k films measured by FF-type Nano-TheMS were consistent with those measured by a FR-type Nano-TheMS arrangement. The new FF arrangement allows for the direct inspection of the thermal conductivity of low-k films without modification of silicon processing procedures.