Control of Copper Morphology on TaN through Surface Point Defects

The downscaling of semiconductor devices makes deposition of copper interconnects challenging. Copper forms non-conductive islands on diffusion barriers such as TaN and this effect worsens as length scales move toward the few-nm. Adding a liner or glue layer, doping the substrate to achieve better adhesion or replacing Cu are being investigated to overcome this challenge. Introducing surface defects, e.g. surface point defects or dopants, can modify the metal nucleation and promote growth of targeted morphologies. Density functional theory (DFT) and ab initio molecular dynamics (aiMD) are used to model surface point defects in TaN and explore how these surface defects can control the adsorption and morphology preference of deposited Cu nanostructures. Formation of nitrogen vacancies is favorable, especially in a hydrogen ambient, with small energy cost, indicating possible control of defects through control of atmosphere during processing. Combining adsorption studies of single atoms and small metal clusters with aiMD simulations of larger metal structures, we show how higher concentrations of surface nitrogen vacancies may limit undesired 3D growth, while a low concentration of vacancies has a negligible effect, promoting 3D island morphology. These results show that morphology control by surface defects is a way to promote target metal morphology.