TaN-Based Combined Barrier+Liner Materials to Beat the Interconnect Bottleneck

Abstract

In order to prolong the lifetime of Cu as an interconnect metal in CMOS devices, as transistors continue to decrease in size, materials that combine properties of diffusion barriers and seed liners are needed. Such a material will have to allow for successful electroplating of Cu and must be as thin as possible in order to facilitate the coating of high-aspect ratio interconnect vias. One possible way to achieve such a material is presented in this study. Through density functional theory we investigate the behaviour Cu on Ru-doped and Ru passivated ε-TaN (1 1 0). Adsorption and diffusion of one and two Cu atoms on these surfaces were studied initially, in order to understand the early stages of film growth. This showed that while adsorption and surface diffusion were more favourable on the Ru passivated surface, Ru dopants act as a nucleation site for Cu atoms and enhance the metal-surface interaction.To understand the growth mechanism of Cu films on these surfaces in more detail, and to discover the optimum Ru content for the surface, large Cu sheets are adsorbed to the Ru passivated surface as well as to Ru-doped surfaces with a variety of surface doping concentrations.On the Ru-doped films, Cu spontaneously transitions into a two-layer structure, while atoms remain in a single layer on the Ru-passivated surface. However, ab initio molecular dynamics and activation energies of pathways for migration of atoms to form further layers show that the Ru dopants inhibit further 3D growth of the Cu structures.