A new alternative self-assembled-monolayer activation process for electroless deposition of copper interconnects without a conventional barrier

Abstract

Amino-terminated, self-assembled monolayers (NH2-SAMs) are widely used for seeding in electroless metallization, and activation is typically performed in an acidic aqueous suspension of colloidal Pd or Au, generating noble-metal catalytic particles of sizes generally exceeding 10 nm. In this study, we develop a new activation process by which aliphatic NH2-SAMs immobilize Ni particles on low-k (SiOCH) dielectric layers, and which involves a cost-effective basic aqueous solution simply containing Ni2+ ions. Rutherford backscattering spectroscopy suggests that the activated SAMs work effectively as diffusion barriers, enabling integration of Cu with SiOCH without interposing a conventional barrier layer. Moreover, as revealed by transmission electron microscopy, the sizes of the Ni particles adsorbed are extremely small (2–3nm), leading to fast nucleation and the formation of void/seam-free Cu interconnects in 60-nm trenches. Based on the results of X-ray photoelectron spectroscopy, a new model of changes in the surface structure (and the phase transitions of the seeds) leading to effective seeding is proposed.