Double-Oxidant-Induced Slurry Reaction Mechanism and Performance on Chemical Mechanical Polishing of 4H-SiC (0001) Wafer

Single-oxidant slurries are prevalently utilized in chemical and mechanical polishing (CMP) of 4H-SiC crystal. Nevertheless, it is a challenge to achieve a high material removal rate (MRR) and surface quality using single oxidant slurries to meet the needs of global planarization and damage-free nanoscale surface processing of SiC wafers. To solve this challenge, a novel method is proposed for SiC CMP processing using the double oxidant slurry. This slurry mainly consists of alumina (Al₂O₃) abrasive particles, potassium permanganate (KMnO₄), potassium persulfate (K₂S₂O₈), and deionized water. Post CMP, MRR is 1045 nm/h calculated by scratch method, and surface roughness Sa is 0.33 nm measured by 3D optical surface morphometer, with the measurement area of 868 μm × 868 μm. Both the MRR and Sa are far better than those under the single oxidant slurry condition. CMP mechanism with double-oxidant slurry conditions is elucidated by energy dispersive spectrometer and X-ray photoelectron spectrometer. Initially, the Si-C bond on the SiC wafer surface was oxidized by KMnO₄, then MnO₂ as the reduction product of KMnO₄ can also catalyze the S₂O₈^2- to further oxidize SiC wafer surface, and eventually the oxidation layers were removed by mechanical action of nano-Al₂O₃ abrasive particles during CMP processing. These findings offer a pioneering approach and novel perspectives to achieve a higher MRR of 4H-SiC CMP, with potential implications for the application in high-performance SiC devices.