Enhancement mechanism of chemical mechanical polishing for single-crystal 6H-SiC based on Electro-Fenton reaction

Abstract

In this study, a quantitative comparison was performed to investigate the change rule of the hydroxyl radical (·OH) concentration and the total ·OH concentration generated by Fenton/Electro-Fenton (EF) reactions using the coumarin capture ·OH method. The relationship between the oxidation activity (total ·OH concentration) of the polishing slurry, coefficient of friction (COF), thickness of the oxide layer, and polishing effect was systematically studied through an immersion oxidation experiment, a friction and wear experiment, and a Fenton/Electro-Fenton chemical mechanical polishing (Fenton-CMP/EF-CMP) experiment. The enhancement mechanism of the EF reaction in the CMP of SiC was also analysed. The results indicated that the application of an electric field significantly improved the oxidation activity and the polishing effect. When the H2O2 concentration was 5.0 wt%, and the applied voltage increased from 0.0 V to 1.5 V and 3.0 V, the oxidation activity increased by 133.47% and 196.24%; COF increased by 9.05% and 13.36%; and material removal rate (MRR) increased by 32.26% and 65.59%, respectively. At a high voltage (3.0 V) and high H2O2 concentration (7.5 wt%), the polishing slurry exhibited the most potent oxidation activity, the oxidised SiC surface was the roughest, the COF and MRR were the highest, and the polishing quality was the best. The application of the electric field accelerated the conversion of Fe3+ to Fe2+ and generated a small amount of the H2O2 in situ, realising the electrical parameter control of the generated total ·OH concentration, such that the EF reaction produced more ·OH than the Fenton reaction, significantly enhancing the oxidation activity of the polishing slurry, which in turn enhanced the oxidation and polishing effects of SiC. The oxidation activity of the polishing slurry, COF, oxide layer thickness, and MRR exhibited a perfect linear correlation; the stronger oxidation activity increased the SiC oxidation effect. A higher SiC roughness after oxidation produced a greater COF, thicker oxide layer, higher MRR after polishing.