Study on polishing mechanisms of BEOL metal interconnects based on chemical and mechanical synergy.

Abstract

Chemical mechanical polishing (CMP) is the sole process capable of achieving the required flatness and surface roughness for photolithography without any obvious distortion in the multilevel metal interconnects. As semiconductor manufacturing advances to the next process node, the introduction of new materials and structures has proposed higher performance standards for polishing slurries, resulting in the slurry composition becoming increasingly critical to the overall polishing process. In this work, ReaxFF-based molecular dynamics (MD) is employed to investigate the copper (Cu) CMP process in various slurries, aiming to uncover the chemical interactions of different components and the atomistic mechanisms involved in Cu atom removal. The results demonstrate that the presence of H₂O₂ cannot only directly oxidize the Cu atoms on the substrate surface, but also inhibit the adsorption of H₂O on the Cu surface and promote the dissociation of the adsorbed H₂O to indirectly oxidize the Cu atoms. The Cu complexes Cu-C₂H₅O₂N and Cu-H₂C₂O₄ are generated during the reaction due to the addition of glycine and oxalic acid, respectively. The oxidation of H₂O₂ and the complexation of glycine and oxalic acid significantly enhance the Cu removal. Furthermore, Cu atoms tend to be removed in the form of clusters, and the removal rate is the highest in the mixed solution of H₂O₂ and glycine. The surface roughness after polishing is 0.082 nm, which closely aligns with the atomic force microscopy (AFM) experimental data of 0.104 nm. This work sheds light on the role of different components in the polishing slurry, which is of great significance to the design of the CMP slurry components for more advanced process nodes.