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Chemical residuals on fused silica after chemical mechanical polishing with silica and ceria have been analyzed. The surface of fused silica terminates with silanol after being polished with silica abrasives but ends up with Ce-O−Si in a ceria-based slurry under the CMP environment. The silanol firstly synthesizes on a fused silica surface polished with ceria, but then further reacts with hydroxyl cerium groups scattering in the slurry forming Ce-O−Si. It also reveals that polishing fused silica with silica abrasives is an alternative way giving an ultra smooth surface.

Whether sapphire or SiC wafer, clear and regular atomic step morphology could be observed all over the ultra-smooth wafer surface via atomic force microscopy (AFM) using our CMP technology. However, towards sapphire and SiC wafers, the variations of atomic step widths and step directions on the whole of wafer surface are different. The step widths and step directions on the different positions of sapphire wafer are uniform, while that on SiC wafer are distinct. Thus, the effects of atomic step width on CMP removal rate of sapphire and SiC wafers were studied. On the other side, the CMP removal model of super-hard hexagonal crystalline wafer to realize atomically ultra-smooth surface is proposed. The variations of atomic step morphology towards different defects on sapphire and SiC wafers surface are analyzed, and the formation mechanism of the defects is discussed.

The application of catalyst nanoparticles in the slurry is developed for chemical mechanical planarization (CMP) of on-axis Si-face (0001) SiC wafer, so as to obtain higher material removal rate (MRR) and defect-free ultra-smooth surface. Fe nanoparticles, as well as Pt/C nanoparticles were used as a catalyst into the slurry, and the polishing experiment results indicate that an Fe catalyst is preferable to CMP of SiC. The removal behaviors of catalyst assisted CMP were studied and the removal mechanism was discussed. The detection results of *OH hydroxyl radicals reveal that the slurries with catalysts could produce *OH radicals so as to induce the oxidation of SiC. The relationship between the removal of SiC wafer by different catalysts and polishing time was investigated. The removal characteristics with different downward pressure and platen rotation speed and relative local temperature were presented. Optical microscope, optical interferometry profiler and atomic force microscope (AFM) were applied to observe the processed surface by the proposed method. Total planarization of the atomically flat defect-free surface with atomic step-terrace structure and extremely low Ra about 0.05. nm was achieved for SiC wafer by using an Fe catalyst slurry. The results affirm that the promising method is helpful to the surface preparation of super-hard and inert materials with high efficiency and high flatness.

Due to its high mechanical hardness and excellent chemical inertness, SiC single-crystal wafer is extremely difficult to realize effectively removed total planarization. Owing to crystalline polarity and anisotropy, material removal rate (MRR) on Si-face (0001) of SiC wafer is significantly lower than C-face (000\bar{1} 1 ̄) for a defect-free surface. In the paper, the slurry containing hydrogen peroxide (H2O2), potassium hydroxide and abrasive colloidal silica, is introduced to chemical mechanical polishing (CMP) of on-axis Si-face 6H-SiC wafer, resulting in acquiring high MRR with 105 nm/h, and atomically flat defect-free surface with atomic step-terrace structure and roughness of 0.0667 nm by atomic force microscope (AFM), in order to satisfy further demands of electronic device fabrication towards substrate wafer performance. The effects of the three ingredients in the slurry towards MRR of SiC wafer, polished surface quality and coefficient of friction in polishing process are studied. Optical microscope, optical interferometry profiler and AFM are used to observe the polished surface. In addition, the CMP removal mechanism of SiC wafer and the formation of ultra-smooth surface are discussed.