Chemical Mechanical Polishing for SiO₂ Film Using Polystyrene@ceria (PS@CeO₂) Core–Shell Nanocomposites

Abstract

In chemical mechanical polishing (CMP) process, to obtain efficiently damage-free surfaces, the structural design of abrasive provides a helpful solution. In this work, highly monodisperse polystyrene (PS) nanospheres [Circa (ca.) 70 nm] were synthesized via a modified soap-free emulsion polymerization. The CeO₂ nanoparticles (ca. 5 nm) were uniformly coated on the surfaces of the PS cores via an in situ chemical precipitation process. The core–shell structured PS@CeO₂ nanocomposites (ca. 90 nm) with a shell thickness of ca. 10 nm were achieved. The samples were further characterized using field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction and thermo-gravimetric analysis. The CMP performance of the as-prepared PS@CeO₂ nanocomposites and conventional CeO₂ nanoabrasives for SiO₂ film formed on Si wafer was investigated by an atomic force microscope and a 3D non-contact surface profiler. The results showed that the substrate polished with PS@CeO₂ nanocomposites exhibited a lower root-mean-square surface roughness (0.15 ± 0.02 nm) and higher material removal rate (189 ± 19 nm/min) than those of conventional CeO₂ nanoabrasives (0.25 ± 0.03 nm, 97 ± 16 nm/min). The improved polishing performance might be attributed to the optimization of the physical contact behavior between particles and wafers.