The mechanism of Fenton reaction of hydrogen peroxide with single crystal 6H-SiC substrate

Abstract

The strong oxidant hydroxyl radical (*OH) generated during Fenton reactions can be used for the chemical mechanical polishing (CMP) of single-crystal silicon carbide (SiC). In this study, we first determine the optimal concentration of the ferrosoferric oxide (Fe3O4) catalyst for the Fenton reaction. Then, we performed Fenton oxidation experiments on 6H-SiC substrates using five groups of reaction solution: hydrogen peroxide (H2O2) solution with four different initial concentrations (5.0, 7.5, 10.0, and 15.0 wt%) and with 1.0 wt% Fe3O4 catalyst and a solution containing 7.5 wt% H2O2 without a catalyst. The concentrations of H2O2, ferrous ions (Fe2+), iron ions (Fe3+), and *OH were monitored during the reaction. Moreover, the surface morphologies and elemental compositions of the SiC substrate before and after oxidation were analysed by scanning electron microscopy and energy dispersive spectroscopy. Finally, the specific components of the oxidation products were analysed by X-ray photoelectron spectroscopy to reveal the reaction mechanism of H2O2 with 6H-SiC. As the reaction proceeded, all the H2O2 concentrations decreased continuously, while the Fe3+ and Fe2+ concentrations increased. After the first 90 min, the H2O2 concentration decreased by approximately 50%–60%, while the Fe2+ concentration increased by approximately 50%–60%. Moreover, the *OH concentration initially increased and then decreased, and the *OH concentration reached its maximum within 100–120 min. At an initial H2O2 concentration of 7.5 wt% with 1.0 wt% Fe3O4, the maximum *OH concentration was approximately 54.4%, 11.8%, 42.5%, and 478% higher than those reached at an initial H2O2 concentration of 5.0, 10.0, and 15.0 wt% with 1.0 wt% Fe3O4 catalyst and in the solution containing 7.5 wt% H2O2 without catalyst, respectively. Surface oxide layers with different thicknesses were found on the SiC substrates oxidised with the different reaction solutions; the layers on the SiC substrates oxidised with 7.5 wt% H2O2 and 1.0 wt% Fe3O4 exhibited a favourable oxidation effect. The initial H2O2 concentration influenced the change in Fe3+, Fe2+, and *OH concentrations. This indicated that further affecting the oxidation effect on the SiC by generating more *OH leads to a greater oxidation effect. The *OH produced damaged the C-Si and C-C bonds on the SiC so that C and Si atoms were separately combined with O atoms to generate CO2 gaseous and SiO2 oxide layers. In this way, SiC substrates were oxidised and corroded, realising the CMP of the SiC with a high removal rate and low roughness.