A nanoclustered ceria abrasives with low crystallinity and high Ce³⁺/Ce⁴⁺ ratio for scratch reduction and high oxide removal rates in the chemical mechanical planarization

Cerium oxide nanoparticles in the size of Ca. 100 nm usually have a degree of crystallinity over 95% and the ratio of Ce³⁺/Ce⁴⁺ at around 40%, which are ascribed to the intrinsic characteristics of atomic hybridization to form a cubic fluorite lattice structure. Therefore, the common form of cerium oxide nanoparticles has high crystallinity and large crystallite size. In this paper, we compared the nanoclustered cerium oxide nanoparticles with the high crystalline ones in terms of surface morphology, crystallinity, surface activity, and oxide removal rates. The NC-ceria and the CF-ceria nanoparticles having similar sizes of 108 and 117 nm with standard deviations of 10.3 and 22.5 nm, respectively. As a novel form of abrasive, the NC-ceria is spherical with crystallite size, L_c = 4.4 nm; crystallinity, X_c = 70.5%, which is quite different from the CF-ceria (L_c = 45.5 nm, X_c = 95.8%). These two different crystal structure provided different properties of Ce³⁺/Ce⁴⁺ ratio and the OH⁻ concentration as 48.4 and 69.4% than CF-ceria as 39.5 and 47.3%, respectively, seemingly due to the propound number of unbound atoms on the surface. As a result, the SiO₂-removal rate of NC-ceria is achieved as 8904 Å/min, which is much higher than that of CF-ceria at 3823 Å/min. Overall, the nanocluster ceria abrasive demonstrates a physically-soft and chemically-active nature, giving excellent SiO₂-removal capability and great potential in scratch suppression in CMP processing.