Characterization of thin metal films via frequency-domain thermoreflectance

Abstract

Frequency-domain thermoreflectance is extended to the characterization of thin metals films on low thermal diffusivity substrates. We show how a single noncontact measurement can yield both the thickness and thermal conductivity of a thin metal film with high accuracy. Results are presented from measurements of gold and aluminum films 20–100 nm thick on fused silica substrate. The thickness measurements are verified independently with atomic force microscope cross sections, and the thermal conductivity measurements are verified through electrical conductivity measurements via the Wiedemann–Franz law. The thermoreflectance thermal conductivity values are in good agreement with the Wiedemann–Franz results for all the films at least 30 nm thick, indicating that our method can be used to estimate electrical conductivity along with thermal conductivity for sufficiently thick films.