Metals for Low-Resistivity Interconnects

A combination of experiments and first-principles simulations are used to search for metals that have a high conductivity at reduced dimensions and are therefore promising candidates for narrow interconnect lines. Epitaxial layers of Cu, W, Ta, Mo, Ru, Co, Ag, Nb and Ni are grown on ceramic single crystal substrates and their resistivity measured in-situ as a function of thickness. Data fitting using the classical Fuchs-Sondheimer model provides values for the electron mean free paths. These values are directly compared to predictions using first-principles calculations of the twenty two most conductive elements. This comparison indicates that the Fuchs-Sondheimer model accurately predicts the resistivity size effect for some metals, but considerably underestimates the resistivity increase for others.