Thermal conductivity measurements of interlevel dielectrics

The thermal conductivity of interlevel dielectrics (ILD) in interconnect structures is an important parameter in determining the temperature rise in the interconnects during use. Numerous researchers have previously shown that the thermal conductivity of thin film dielectrics can be significantly lower than that of bulk materials. As new materials, such as low-dielectric constant materials, are considered for use as ILD's, methods are needed for measuring the thermal conductivity of the these materials to determine whether they can adequately conduct heat away from interconnect lines. Many methods reported in the literature use patterned metal lines atop the dielectric on a Si substrate as combination Joule heaters and temperature sensors, and extract the thermal conductivity from a model of heat conduction through the dielectric to the substrate. One drawback of these methods is the lack of agreement of the conductivity determined from the different techniques. For example, a thermal conductivity ranging from 0.6 to 1.4 W/m-K was calculated for a 1.25 mu m thick PTEOS oxide using five different methods on the same test structure. In this paper we present a unique combination of test structures, experimental methods, and heat conduction models that highlight the limitations of some of the models and methods. We also show good agreement in the thermal conductivity determined from both an experimental method and a finite element model, and suggest that these two techniques yield an accurate measure of the thermal conductivity of thin film dielectrics.