It is well known that the ceria particles are used in CMP as abrasive particles and represent high removal rates of oxide films than silica particles due to the ability to interact with the surface of the SiO2 layer. The ceria abrasive nanoparticles are also desirable for the CMP of shallow trench isolation (STI), due to their high selectively of silicon dioxide over silicon nitride. However, the ceria particles have irregular shape and are easy to aggregate each other due to their high specific gravity. Therefore, the ceria abrasives used in CMP have negative effects on the polished films such as excessive scratches and defects.
To make up for the weak points of the ceria abrasives, there is a method to coat CeO2 on the SiO2 nanoparticles that have spherical shape and low specific gravity. In this study, the microemulsion method was introduced to make CeO2 thin film deposition on the SiO2 nanoparticles. Microemulsions are isotropic, clear or translucent, thermodynamically stable dispersions of oil, water, emulsifier, and often a small amphiphilic molecule called a cosurfactant. These surfactant-covered entities (referred to as Water-in-Oil (W/O) microemulsion droplets) offer a unique microenvironment for inorganic precipitation reactions. In this experiment, the silica nanoparticles were synthesized first, and ceria was thin coated on the silica by adding ceria precursor to microemulsion which contain silica nanoparticles inside the micelles. In this work, we conducted a systematic investigation of the effect of the surfactants species, the amount of cosurfactants and the pH of the microemulsion system.