Semi-insulating 4H-SiC(0001) has high hardness and high chemical inertness, making it difficult to obtain high material removal rates during chemical mechanical polishing (CMP). In this paper, the role of chemical additive ferric nitrate in semi-insulating 4H-SiC(0001) CMP with α-alumina as abrasive and KMnO4 as oxidant is discussed. The results showed that 0.5 wt% ferric nitrate can increase the removal rate of semi-insulating 4H-SiC(0001) by 34%, while the semi-insulating 4H-SiC(0001) surface roughness Ra was reduced from 0.123 to 0.110 nm. The key point was that the coefficient of friction of the polishing slurry was effectively reduced, which was beneficial to the ploughing effect of the α-alumina abrasive with vermicular thin section morphology which had the highest removal rate. In addition，the chemical composition of 4H-SiC (0001) corrosion layer was analyzed by X-ray photoelectron spectroscopy under different corrosion conditions. Si 2P spectrum analysis showed that O atoms only attack C atoms to produce Si-C-O structure under acidic conditions, whereas, with the addition of ferric nitrate, O atoms not only attacked C atoms, but also attacked Si atoms to produce softer SiO2 and Si-Ox-Cy structures. The chemical mechanical polishing mechanism of Semi-insulating 4H-SiC (0001) is also given.

LiTaO3 has piezoelectric, ferroelectric, and pyroelectric optical properties with a broad transparent range from ultraviolet to infrared. In order to ensure good performance of the LiTaO3 substrate, the surface of the LiTaO3 substrate must be smooth. Chemical mechanical polishing has been used for planarization of integrated circuits or to obtain substrates of high surface quality. In this paper, neotame was studied as an additive for LiTaO3 slurry, which plays an important role in the polishing process. In addition, we show that different pH and different concentrations of neotame have a strong influence on the polishing rate, the surface roughness of the LiTaO3 substrate after polishing is different, and the surface roughness of the LiTaO3 substrate can be reduced to 0.112 nm. More importantly, neotame could improve the work-life of the polishing slurry and reduce the coefficient of friction, thereby reducing the fragmentation rate. Finally, the possible chemical reaction mechanism of neotame to accelerate polishing efficiency was given.

As two typical representatives of super-hard materials, the processing of sapphire and silicon carbide has always been a hot spot. Chemical mechanical polishing technology is the only way to achieve global planarization, and it has also become one of the most important processes for precision machining of these materials. We have studied the relationship between the removal rate and surface roughness of sapphire and 4H-SiC (0001) and the size distribution and pH of the alumina slurry. More importantly, we explored the negative effect of Na+ on the removal rate of an alumina-based sapphire polishing slurry, and the more negative effect of Na+ on the removal rate of an alumina-based silicon carbide polishing slurry and the surface state of SiC(0001). Finally, the polishing mechanism of sapphire with alumina used as a brasive is given.