Computational Investigation of the Effect of Thermal-Induced Atomic Motion on Resistivity of Copper Interconnects

Increasing transistor density is one of the most effective ways to increase chip performance. However, this downscaling effect causes an increase in resistivity in conducting lines as we approach the length of the mean free path of the material. The resistivity of an interconnect (IC) can be predicted from the combination of bulk resistivity and scattering-induced resistivity increase. While many theoretical works have been done in this area, we still lack an atomic-level understanding of how thermal-induced motion in ICs affects the transport properties of materials. In this talk, we will focus on copper (Cu), an ideal conductor. Three ab initio molecular dynamics (AIMD) trajectories were run at 218 K (-55 °C), 300 K (27 °C), and 540 K (267 °C) over 20 picoseconds (ps). Through these AIMD trajectories, atoms were displaced from their equilibrium positions by varying amounts depending on the temperature. From these trajectories, structures were generated from the snapshots every 0.1 ps over the last 10 ps of the trajectories, and electron transport calculations were performed with the non-equilibrium Green's function approach combined with density functional theory (NEGF-DFT). While 218 K and 300 K share a similar level of minor reduction in transmission coefficient compared to pristine structure, a significant transmission coefficient drop was observed at 540 K. Furthermore, trajectories with a roughened surface created by atomic vacancies and oxygen-reacted surface were simulated as well. Through these simulations, we can establish a connection between how thermal effects, roughness, profile and reaction with oxygen affect the transport properties of the material.