Electro-chemical mechanical polishing of silicon carbide

In an effort to improve the silicon carbide (SiC) substrate surface, a new electro-chemical mechanical polishing (ECMP) technique was developed. This work focused on the Si-terminated 4H-SiC (0001) substrates cut 8° off-axis toward 〈1120〉. Hydrogen peroxide (H₂O₂) and potassium nitrate (KNO₃) were used as the electrolytes while using colloidal silica slurry as the polishing medium for removal of the oxide. The current density during the polishing was varied from 10 μA/cm² to over 20 mA/cm². Even though a high polishing rate can be achieved using high current density, the oxidation rate and the oxide removal rate need to be properly balanced to get a smooth surface after polishing. A two-step ECMP process was developed, which allows us to separately control the anodic oxidation and removal of formed oxide. The optimum surface can be achieved by properly controlling the anodic oxidation current as well as the polishing rate. At higher current flow (>20 mA/cm²), the final surface was rough, whereas a smoother surface was obtained when the current density was in the vicinity of 1 mA/cm². The surface morphology of the as-received wafer, fine diamond slurry (0.1 μm) polished wafer, and EMCP polished wafer were studied by high-resolution atomic force microscopy (AFM).