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

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.