Control of Cu morphology on TaN barrier and combined Ru-TaN barrier/liner substrates for nanoscale interconnects from atomistic kinetic Monte Carlo simulations

Abstract

The miniaturization of electronic devices brings severe challenges in the deposition of metal interconnects in back end of line processing due to a continually decreasing volume available for metal deposition in the interconnect via. Cu is currently used as the interconnect metal and requires barrier and liner layers to prevent diffusion into silicon and promote deposition of smooth conducting metal films, respectively. However, these take up a significant volume in the interconnect vias, which are already extremely narrow due to the high aspect ratio required. Designing combined barrier/liner materials provides opportunities to promote deposition of smooth films and avoid islanding and frees up precious volume to deposit the required amount of interconnect metal. We present here the first atomistic kinetic Monte Carlo (kMC) investigation of the potential of Ru-modified TaN as a dual-function barrier/line material to promote 2D morphology of deposited Cu enabling optimization of the limited available interconnect volume. The kMC simulations use Density Functional Theory (DFT) activation barriers to predict the role of the combined barrier/liner material on the morphology of deposited Cu and give, for the first time, a tool to predict metal deposition on technologically important substrates. We study Cu deposition at different partial pressures on a series of substrates, including unmodified TaN and TaN with 25% or 50% surface Ru incorporation, at deposition temperatures of 300 K, 500 K and 800 K. The deposition simulations predict Cu film roughness, island size and number, substrate exposure area (as a measure of 2D vs. 3D morphology), layer occupation rate, compactness (as a measure of film quality) and the impact of annealing. As-deposited Cu on unmodified TaN exhibits significantly higher roughness and substrate exposure areas, demonstrating island formation...