Ultralow-k Amorphous Boron Nitride Film for Copper Interconnect Capping Layer

We report the feasibility of ultralow- ${k}$ amorphous boron nitride ( $\alpha $ -BN) film as a new capping layer for copper (Cu) interconnects. $\alpha $ -BN thin films were successfully deposited using a plasma-enhanced chemical vapor deposition (PECVD) process. The CVD-grown $\alpha $ -BN showed a ${k}$ -value as low as 2.0 at 3 nm thickness, low leakage current density ( $\sim 7\times 10^{-{8}}$ A/cm2), and high breakdown field ( $\sim $ 8.8 MV/cm) comparable to a conventional SiN blocking layer. The $\alpha $ -BN has excellent thermal stability up to 1000 °C, implying that the film can be used not only for the back-end-of-line (BEOL) but also for the front-end-of-line (FEOL) processes. A 7-nm-thick $\alpha $ -BN film successfully blocked Cu diffusion at temperatures up to 500 °C. The $\alpha $ -BN film also showed excellent adhesion to Cu, with an adhesion energy of 2.90 ±0.51 J/ $\text{m}^{{2}}$ between $\alpha $ -BN and Cu. The COMSOL multiphysics simulation predicted that, compared to a conventional SiN capping layer, an $\alpha $ -BN capping layer would reduce interconnect RC delay by up to 17%. The $\alpha $ -BN was proven to be a promising new candidate for a capping layer to reduce RC delay in Cu interconnect systems.