| The early and most commonly used abrasive in chemical mechanical polishing (CMP) slurry is silica (SiO2) slurry. SiO2 abrasive slurry possesses the advantages of low preparation cost, simple technology and high polishing selectivity, but cannot polish the SiO2 material of multilayer wiring and possesses the lowest polishing rate among the sole abrasive slurries, which restricts its application range. If we make the SiO2 and CeO2 compound, and then prepare the SiO2/CeO2 composite abrasive slurry, the problems what discussed above are expected to be solved and the application range of SiO2 abrasive slurry is expected to be extended. Meanwhile, in application of CMP technology, the dispersion stability of slurry has great effect on storage, transportation, polishing effect, and so on, and the performance of dispersion stability has a close relationship to the property of abrasive particles in different solution. Therefore, we systematically study the synthesis and the dispersion stability of SiO2/CeO2 composite particles, investigate the optimum condition of preparing SiO2/CeO2 CMP slurry possessing low concentration and high dispersion stability, and provide some valuable clues for developing new composite abrasive CMP slurries.Mesoporous SiO2 with different specific surface areas were synthesized by the chemical precipitation method from sodium metasilicate (Na2SiO3), hydrochloric acid (HCl) and cetyltrimethyl ammonium bromide (CTAB). The influence factors, such as pH, concentration of Na2SiO3, concentration of HCl and reaction temperature, on specific surface area were investigated by the orthogonal experiment. Mesoporous SiO2 with a BET specific surface area of 1041.38m2/g and an average pore size of 5.78nm was synthesized under the condition as: amount of CTAB 10wt%, pH=8, concentration of Na2SiO3 0.4mol/L, concentration of HCl 1.0mol/L, reaction temperature 30℃.SiO2 particles were synthesized by sol-gel method by using tetraethylorthosilicate (TEOS) as silicon source, CH3CH2OH as solvent and ammonia (NH3·H2O) as catalyst. The effect of the ratio of the materials on the particle size and distribution of SiO2 particles was researched by the laser particle size analysis. The results show that the particle size of SiO2 particles decreases and the size distribution of SiO2 particles becomes narrow as the amount of NH3 and H2O decreases and the amount of ethanol increases. The optimum conditions for synthesizing SiO2 particles were: molar ratio of TEOS to NH3 1:4, molar ratio of TEOS to CH3CH2OH 1:20, molar ratio of TEOS to H2O 1:30.Using SiO2 particles synthesized by sol-gel method as cores, cerium nitrate hexahydrate (Ce(NO3)3·6H2O) as a cerium source, ammonium carbonate monohydrate ((NH4)2CO3·H2O) as the precipitating agent and sodium dodecyl benzene sulfonate (SDBS) as the dispersant, the core-shell SiO2/CeO2 composite particles were successfully synthesized through a chemical precipitation method by controlling the reaction factors under the following conditions: 0.05mol/L SiO2, 0.015mol/L Ce(NO3)3, reacting for 2h, aging for 5h. Under this synthesis conditions, the core-shell SiO2/CeO2 composite particles whose diameter is about 300-350nm have a uniform size distribution, a spherical morphology and an excellent monodispersity. The thickness of the CeO2 shell is about 30 nm. A CeO2 can be primarily coated onto the surface of SiO2 particle to form a shell, with a little CeO2 deposition on the SiO2 core. Isoelectric point of SiO2/CeO2 composite particle was about 5.9, which displayed a significant shift toward pure CeO2.The dispersion stability of SiO2/CeO2 composite particles in water medium was studied. Dispersion experimental results indicate that the dispersion stability of SiO2/CeO2 suspension is affected obviously by pH value and in consistency with zeta potential. Dispersion mechanism is static repulsion interaction of double electrical layer. When pH value is less than 4 or more than 10, the zeta potential and absorbance of SiO2/CeO2 suspension will reach a higher value, corresponding better dispersion stability. The dispersion stability of SiO2/CeO2 suspension is improved as the increase of mechanical stirring rate and ultrasonic wave time. The dispersion effect of ultrasonic wave on SiO2/CeO2 composite particles is markedly superior compared with mechanical stirring. The anion surfactant SDBS and the nonionic surfactant poly ethylene glycol (PEG) 4000 can improve the dispersion stability of suspension. A suspension with SiO2/CeO2 at 0.04wt% was added in 0.05g/L anionic surfactant SDBS, and its pH value was adjusted within the range of 10-10.5. In this condition, the stable suspension without sedimentation time was successfully obtained. The addition of surfactants can increase the repulsion interactions of electrical double layer, hydration shell and steric hindrance, and decrease the van der waals attraction interactions.A series of mixed type SiO2-CeO2 composite particles with different cerium and silica (Ce/Si) molar ratios were synthesized via a coprecipitation method using TEOS, Ce(NO3)3 and NH3-H2O as raw materials. The results show that the crystal of the CeO2 grows up gradually and the average crystallite size of the CeO2 decreases with the increase of amount of CeO2. The dispersion stability of SiO2-CeO2 composite particles with a Ce/Si molar ratio of 1 was studied. It is found that the pH value of mixed type SiO2-CeO2 CMP slurry should be controlled in 4 or 10.
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