Optimizing of the Colloidal Dispersity of Silica Nanoparticle Slurries for Chemical Mechanical Polishing

The colloidal silica is used as the abrasive for the copper Chemical Mechanical Polishing slurry in integrated circuit multilayer copper wiring. The aggregation of colloidal silica in the slurries tends to aggregate spontaneously, resulting in the continuous changes of the polishing effect, such as scratch defects, removal rate, etc. This situation can lead to the potential instability of the polishing slurry, which should be avoided in industrial production. In this paper, the aggregation and dispersion properties of polishing slurries were systematically studied, and an scheme was proposed to improve the dispersion of slurries to prevent agglomeration. These affecting factors including slurries’ pH, Potassium nitrate and Sodium Polyacrylate were assessed with Large particle counts, Zeta potential and Particle size. Slurry’s pH at 9.6 had a lower Zeta potential which meant a higher dispersion colloidal silica compared to other pH of slurries. And the dissolution of colloidal silica was verified by UV-vis experiment. Sodium dodecyl sulfate, Dodecyl trimethyl ammonium chloride and Primary Alcobol Ethoxylate-15 were analyzed for their dispersion in slurries from the point of view of static electricity and steric hindrance, and the synergistic mechanism of mixed Sodium dodecyl sulfate and Primary Alcobol Ethoxylate-15 on slurries dispersion was highlighted. In addition, the effect of the improvement of slurry dispersion on reducing scratching defects on the surface of polished copper blanket was also tested in this paper.