Newly designed colloidal silica for copper chemical mechanical polishing in electronic packaging

Due to the rapid development of IC techniques, it is challenging to follow the Moore’s law any longer for the IC fabrication as the feature size of FETs has been close to the physical limitation for quantum effect. As the technology beyond the Moore’s law, the advanced electronic packaging has become the alternative approach for persisting the enormous increment of FET density in the chips. In the IC fabrication and advanced electronic packaging (RDL), the global planarization of the TSV copper interconnects can only be achieved via the chemical mechanical polishing (CMP). In the Cu-CMP process, the slurry used for the polishing is mainly composed of colloidal silica, oxidizer, coordination ligand, inhibitor and the surfactant. The mechanical abrasion in the CMP is mainly supported by the colloidal silica, where the particle size, size distribution, the zeta potential, and the pH are the main factors that could determine the material removal rate (MRR) and the surface uniformity. In generally, Cu-CMP slurries mainly contains colloidal silica below 100 nm, under which the MRR is inconvenient to be further promoted. On the other hand, the Cu-CMP slurries are always adjusted to low pH (acidic) or large pH (alkalic) dispersions, which is harmful to the CMP instruments or the human health.In this paper, the colloidal silica with monodispersed sub-micron particle size and high purity was synthesized by a new approach assisted by the amino acids. The newly designed colloidal silica has the controllable particle size, monodispersed size distribution, large absolute zeta potential as well as the neutral pH. The CMP experimental results revealed that high MRR, high long-term stability, low surface roughness and low particle residues could be achieved via applying the newly designed colloidal silica, which should be promising for the global planarization of TSV copper interconnects for the advanced electronic packaging.