Investigation of oxidation mechanism of SiC single crystal for plasma electrochemical oxidation

Abstract

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.