High-efficiency wafer-scale finishing of 4H-SiC (0001) surface using chemical-free electrochemical mechanical method with a solid polymer electrolyte

Abstract

Silicon carbide (SiC) has been extensively studied for applications in next-generation high-power electronic devices. High-quality and low-cost electronic devices require a surface finishing process that can produce smooth and defect-free 4H-SiC (0001) surfaces. However, SiC surfaces are difficult to remove because of their extremely high mechanical strength and chemical stability. Herein, we present a high-efficiency, wafer-scale, chemical-free finishing process for a 4H-SiC (0001) surface using electrochemical mechanical polishing (ECMP) with a solid polymer electrolyte (SPE). The ECMP method comprises electrochemical oxidation at the SiC/SPE interface and subsequent oxide removal by CeO2 particles. Electrolysis with a SiC (anode)/SPE/cathode electrochemical system demonstrated that the use of SPE as an alternative to liquid electrolytes allows the efficient electrochemical oxidation of highly inert SiC (0001) surfaces without requiring any chemicals. The ECMP process achieved a high material removal rate for SiC (0001) in the range of 1.8–9.2 μm/h, although strongly dependent on a 50 to 450 mA electrolytic current. Moreover, an electrolytic current of 250 mA produced a smooth and defect-free surface with a sub-nanometer-scale roughness (0.68 nm Sa) and excellent uniformity over an entire 2-inch SiC (0001) surface. Atomic force microscopy observations showed that ECMP under a low electrolytic current (30 mA) combined with subsequent CeO2 polishing without electrolysis can help improve microscale surface morphologies. The proposed ECMP, which produces a smooth and uniform surface without requiring chemicals, is a highly efficient and environmentally friendly finishing process for the fabrication of SiC wafers.