Electroless Diffusion Barrier Process Using SAM on Low-k Dielectrics

A wet process based on electroless deposition is proposed for the formation of a diffusion barrier layer for Cu wiring in ultra-large scale integration (ULSI) technology. The diffusion barrier layer is formed on a low-dielectric constant (low-k) inter level film. In this process, a Pd-activated self-assembled monolayer as a seed/adhesion layer was used as a key step to allow electroless deposition on a dielectric film. The effectiveness of this approach was demonstrated by depositing an electroless NiB layer as the diffusion barrier layer. The electrolessly deposited NiB layer showed a uniform surface, a small grain size, and a high adhesion when deposited on various common inter level dielectric materials with low dielectric constant. The electrolessly deposited NiB layer formed on the low-k dielectric film by this method showed a high thermal stability of the effectiveness as a barrier to Cu diffusion at temperatures up to 400°C for 30 min. The electroless process was found to be reproducible and did not affect dielectric properties of the underlying insulator.