Polishing Performance Of TiO₂and TiO₂/CeO₂Composite Oxide With Core/Shell Structure

Chemical mechanical polishing (CMP) is the best planarization technology of manufacturing technology of ultra-large-scale integrate circuits(ULSI). At present, nano-SiO2, nano-CeO2and their composite oxides are used in silicon wafer polishing. With the increase of surface quality requirement of silicon substrate for integrated circuits, and the high price of rare earth raw materials, seeking new polishing material is becoming a hot spot of CMP. In this paper, anatase titanium dioxide and titanium cerium core/shell structure composite oxide were used in polishing of silicon wafer, LCD and K9glasses. The effect of process conditions on polishing performance was studied, and the reasons for the improvement of polishing performance were discussed.Anatase titanium dioxide powders were used in silicon wafer polishing. Effect of pH value, the concentration of TiO2and the volume fraction of monoethanolamine (MEA) in polishing slurry on MRR of n-type Si(111) were studied. The optimal conditions for polishing n-type Si(111) were determined to be slurry pH11.5, TiO2concentration in slurry0.5%, MEA volume fraction in slurry0.035%-0.045%. With these conditions, a high MRR of113nm/min was obtained, the surface of polished silicon wafer is very flat and smooth. The results showed that the addition of MEA into titanium dioxide slurry increased MRR value of polishing silicon wafer by20to40%. Based on the TPR profiles of powders and UV spectra of polishing slurry, it was suggested that the significant increase of MRR is due to the generation of hydroxyl radicals with strong ability of oxidation on the surface of titanium dioxide promoted by MEA, which accelerated the formation of a soft layer on silicon wafer surface.The effects of pH value and solid concentration of anatase titanium dioxide powders on the polishing of LCD and K9glasses were studied, and the optimal conditions were found to be pH6.0, solid content of TiO22.5%. The results showed that the MRR value for polishing LCD glass by titanium dioxide was greater than that K9glass, indicating that anatase titanium dioxide is a suitable polishing material for LCD glass.TiO2/CeO2core/shell composite powders were prepared by hydrolysis method using TiO2as core, cerium nitrate as cerium source, sodium hexametaphosphate as surfactant, dilute sodium hydroxide as pH adjustment agent. The optimum synthesis conditions and polishing techonology were determined. XRD, SEM and TEM results showed that TiO2/CeO2composite powders with good core/shell structure were obtained. The obtained composite oxide powders showed high polishing performance for silicon wafer, because the coating of CeO2on TiO2surface can alter the oxidation property of CeO2, thereby promoting the chemical reaction during the polishing process and increasing the material removal rate.