Thickness-Dependent Optical Properties of Metallic Thin Films and Their Correlation with Thermal Conductivity

The semiconductor industry stands as a cornerstone of modern technology, and its relentless pursuit of miniaturization, efficiency, and performance hinges upon the precise control and understanding of materials used in electronic devices. Within this context, the study of thin films of metals takes on paramount significance. These films play a pivotal role in various semiconductor applications, as they are utilized not only as fundamental components in electronic devices but also as essential elements in the thermal management of these devices. As electronic components become increasingly compact and powerful, the efficient dissipation of heat generated during operation has become a critical challenge. Understanding the optical and thermal properties of thin metal films is instrumental in addressing these challenges, as it offers valuable insights into their potential as heat-dissipating materials and their influence on the performance and reliability of semiconductor devices.<br/>In this study, we perform precise spectroscopic ellipsometry measurements on thin films of several metals that are of unique importance for electronic devices, including copper, iridium, ruthenium, and tungsten. Using these measurements, we determine the optical properties of these metallic thin films across a broad spectral range throughout the infrared and UV-Vis region. Through meticulous analysis involving the Drude free-electron model, we quantify variations in relaxation times and plasma energies in relation to film thickness. Furthermore, our investigation extends to exploring the intriguing interplay between size-dependent relaxation times, as derived from the Drude model, and the thermal conductivity of these metallic thin films, as measured using a thermoreflectance-based thermal conductance and ultrafast pump-probe technique. Our findings are instrumental in enhancing our understanding of these materials' behavior, with potential implications for the development of advanced electronic components.