Silicon carbide (SiC) is a hard-to-machine material due to its high hardness and chemical stability, and usually an essential step in chemical mechanical polishing (CMP) is to modify the SiC surface without introducing damage or other elements, then to polish the modified surface. For high quality and high efficiency surface modification of SiC, a green and promising oxidation approach named plasma electrochemical oxidation (PECO) is proposed. Experiments were conducted to investigate the oxidation mechanism of PECO to enable its application for CMP. The oxidized surface was detected by scanning electron microscope (SEM) and atomic force microscopy (AFM), many atomic-scale protuberances were confirmed to be introduced in the PECO process. Through the analysis of energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), it is proved that the SiC surface has been oxidized into SiO₂ and a transition layer (silicon oxycarbide) is formed between SiO₂ and SiC. Based on the analysis of the cross section image of the oxidized layer, electrolyte–SiC interface chemical reaction and oxidation layer formation mechanism are illustrated to explain the oxidation mechanism. Silicon dioxide growth process model is proposed and illustrated that the phrase of protuberances growth change from charge transfer to diffusion. The present work offers an alternative approach to modify SiC surface, and provides a reference for chemical and mechanical synergetic effect applied in CMP.

Single-crystal 4H-SiC is a typical third-generation semiconductor power-device material because of its excellent electronic and thermal properties. A novel polishing technique that combines plasma electrolytic processing and mechanical polishing (PEP-MP) was proposed in order to polish single-crystal 4H-SiC surfaces effectively. In the PEP-MP process, the single-crystal 4H-SiC surface is modified into a soft oxide layer, which is mainly made of SiO₂ and a small amount of silicon oxycarbide by plasma electrolytic processing. Then, the modified oxide layer is easily removed by soft abrasives such as CeO₂, whose hardness is much lower than that of single-crystal 4H-SiC. Finally a scratch-free and damage-free surface can be obtained. The hardness of the single-crystal 4H-SiC surface is greatly decreased from 2891.03 to 72.61 HV after plasma electrolytic processing. By scanning electron microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS) observation, the plasma electrolytic processing behaviors of single-crystal 4H-SiC are investigated. The scanning white light interferometer (SWLI) images of 4H-SiC surface processed by PEP-MP for 30 s shows that an ultra-smooth surface is obtained and the surface roughness decreased from Sz 607 nm, Ra 64.5 nm to Sz 60.1 nm, Ra 8.1 nm and the material removal rate (MRR) of PEP-MP is about 21.8 μm/h.