Polystyrene/CeO ₂ Core/Shell Abrasives for High-Quality 4H-SiC Surface in ECMP: The Effects of Shell Thickness

Polystyrene (PS)/CeO ₂ core/shell abrasives with different shell thicknesses were synthesized and exploited to obtain high-quality 4H-SiC surface in electro-chemical mechanical polishing (ECMP). The synthesized PS/CeO ₂ abrasives were observed by a scanning electron microscope (SEM); the results showed PS/CeO ₂ with a similar core (200 nm) but different shell thicknesses (8.5, 15.5, 20.5 and 27.5 nm) were obtained. Young’s moduli of these abrasives were measured by an atomic force microscopy (AFM) considering the bottom deformation of abrasives. The effects of shell thickness on the contact area between the abrasive and the wafer surface, and on the indentation depth of the abrasive into the wafer surface were calculated. The indentation depth, representing surface quality, was compared with the surface roughness obtained from the following ECMP verification tests. The results characterized by a microscope and an AFM showed that surface quality polished by PS/CeO ₂ (little scratches; R _a : 2.388–3.181 nm) was better than that polished by CeO ₂ (many scratches; R _a : 3.661 nm), and that effects of shell thickness on polishing quality agreed well with the established theoretical model. Mechanisms of improving surface quality polished by core/shell abrasives and the effects of shell thickness on polishing quality were explained by the applied elastic-contact theoretical model.