Design of ceria grafted mesoporous silica composite particles for high-efficiency and damage-free oxide chemical mechanical polishing

Highlights: • The CeO₂-based particles with mesoporous silica cores were designed and synthesized. • The effect of core structure of composite abrasives on oxide-CMP was discussed. • The _mSiO₂/CeO₂ composite abrasives achieved high-efficiency and damage-free polishing. • The _mSiO₂/CeO₂ composite particles presented an improved structural stability. • The enhanced MRR might be related to the crystallinity and Ce³⁺ content of CeO₂. Chemical mechanical polishing or planarization (CMP) is a material removal process dominated by mechanical and tribo-chemical assisted friction and wear. The choice of abrasive plays a key role in this process. In this work, the _mSiO₂/CeO₂ composite particles, consisting mesoporous silica (_mSiO₂) cores and CeO₂ nanoparticle coatings, were designed and introduced into oxide chemical mechanical polishing (CMP) as novel abrasives. The abrasives were further characterized in terms of X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDX) techniques. Five different abrasive systems were tested in the oxide CMP processes, and their performances were evaluated in terms of material removal rate (MRR) and surface roughness. Particularly, the effects of inner cores of composite abrasives were investigated by comparing _mSiO₂/CeO₂ (meso-silica cores), _sSiO₂/CeO₂ (solid-silica cores), and PS/CeO₂ (solid-polystyrene cores). As confirmed by TEM and XPS, the _mSiO₂/CeO₂ composite particles revealed an improved structural stability with respect to PS/CeO₂ hybrids, resulting from the formation of Ce-O-Si chemical bonding between SiO₂ and CeO₂ after high-temperature calcination. Overall, the composite abrasives resulted in a decreased surface roughness and reduced mechanical damage after CMP due to the spring-like effect coming from the elastic component of the PS or the _mSiO₂ cores, compared with the conventional rigid inorganic ceria abrasives or the mixed compounds (_mSiO₂+CeO₂). In addition, the _mSiO₂/CeO₂ composites exhibited a comparable surface roughness (0.20 vs 0.18 nm) and topographical variation with respect to PS/CeO₂ hybrids. However, the material removal rate for the _mSiO₂/CeO₂ abrasives (64 nm/min) was about three times larger than that of the PS/CeO₂ abrasives (19 nm/min) under the same CMP conditions. The enhanced removal rate might be related to the improved crystallinity of CeO₂ particles and the increased content of Ce³⁺ ions at the CeO₂ surfaces.