Well-rounded CeO₂ nanoparticles

The makers of advanced integrated circuits could soon get smoother silicon wafers with far fewer defects, thanks to a new technique for growing cerium oxide (ceria) nanoparticles. To achieve the smoothness needed for advanced circuitry, electronics makers polish silicon wafers with an abrasive solution. Ceria nanoparticles are frequently used as the abrasive material in this chemical mechanical planarization process. Because of the way they are synthesized, most ceria nanoparticles tend to have irregularly faceted polyhedral shapes (shown, left), which can scratch the silicon and create defects. Now, a group led by Xiangdong Feng of Ferro Corp., in Independence, Ohio, and Zhong Lin Wang of Georgia Institute of Technology have developed a large-scale synthesis of single-crystal ceria nanospheres (Science 2006, 312, 1504). These tiny spheres act like ball bearings, the researchers say, polishing the silicon with 80% fewer defects. To achieve the spherical shape, the team doped the ceria system with titanium. This allowed the inner ceria core to evolve into a single-crystalline sphere (shown, right) without faceting. This principle, Feng and Wang say, could be applied to other oxide systems.