Converting Ceria Polyhedral Nanoparticles into Single-Crystal Nanospheres

Abstract

Ceria (CeO2) nanoparticles are one of the key abrasive materials for chemical-mechanical planarization (CMP) of advanced integrated circuits. However, CeO2 nanoparticles synthesized by all existing techniques are faceted with irregular faceted-shapes, and they scratch the silicon wafers with increased defect concentrations. Here, we show for the first time an innovative approach for large-scale synthesis of spherical, single-crystal, CeO2 nanoparticles. Our synthetic strategy involves doping the CeO2 system with titanium, using flame temperatures that facilitate crystallization of the CeO2, yet retains the TiO2 in a molten state. In conjunction with Molecular Dynamics simulation, we show that under these conditions, the inner CeO2 core evolves in a single-crystal spherical-shape without faceting, because, throughout the crystallization, it is completely encapsulated by a molten 1-2 nm shell of TiO2, which, in liquid state, minimizes the surface energy. The single-crystal nanospheres reduce CMP defects by 80% and increase the silica removal rate by 50%, which will facilitate precise and reliable mass-manufacturing of chips for nanoelectronics at a precision of sub-nanometers. The principle demonstrated here could be applied to other oxide systems.