AFM and XPS studies on material removal mechanism of sapphire wafer during chemical mechanical polishing (CMP)

The material removal mechanism of sapphire wafer during chemical mechanical polishing has been studied through X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements. XPS results indicate that alumina silicate (Al₂Si₂O₇·2H₂O) is generated on the polished sapphire surface by SiO₂ slurry, otherwise alumina hydrate (AlO(OH)) on the polished surface by H₂O solution. Meanwhile, ultra-smooth polished surface with extremely low Ra of below 0.1 nm and atomic step structure morphology via AFM is realized using SiO₂ slurry. Through investigating the variations of the surface characteristics polished by different ingredients via the morphology and force curve measurements, it’s reveals that the product-aluminum silicate with stronger adhesion and lower hardness is more readily to generate and be removed than the product-alumina hydrate induced by H₂O. Thus, except for atomic scale mechanical abrading, the abrasive SiO₂ nanoparticle is used for anticipating in the chemical reaction, resulting in superior surface finish of sapphire wafer with high efficiency.