Sustainable Electrochemical Mechanical Polishing (ECMP) for 4H-SiC wafer using chemical-free polishing slurry with hydrocarbon-based solid polymer electrolyte

Abstract

Large-diameter single-crystal silicon carbide (SiC) wafers with good surface quality are desirable to dramatically improve the performance of SiC-based power electronic devices. However, the preparation of such wafers using a strong oxidative polishing slurry has the limitations of low material removal rate (MRR) and high environmental impact. Electrochemical–mechanical polishing (ECMP) initiates surface removal by electrochemical oxidation without using harsh chemicals, making it an alternative with low environmental impact to conventional polishing. Herein, we propose the use of polystyrene sulfonic acid (PSS), a hydrocarbon-based polymer electrolyte without perfluoro compounds, for ECMP. The SiC surface was effectively oxidized by ECMP using PSS. The effects of the polyelectrolyte crosslinking treatment on the lifetime of polyelectrolyte-incorporated nonwoven cloths were investigated. The optimum electrolytic and mechanical conditions yielded high MRRs of 37 and 14 µm/h for 2- and 4-inch SiC wafers. Moreover, the surface morphologies of the growth face and nonfacet areas was discussed. The wafer-scale evaluation demonstrated the roughness reduction to 0.85 nm Sa (average) after 15-min ECMP of the 4-inch wafer. The polishing-induced residual stress was investigated using microscale and wafer-scale Raman mapping. Overall, the proposed ECMP process offers significant advantages in terms of speed, cost-effectiveness, and environmental impact.