Fabrication Mechanism of Atomically Flat n-Type 4H-SiC (000-1) Surfaces by Electrochemical Method

Abstract

We have developed a rapid abrasive-free SiC planarization method which simply involves contact of a rotating Pt disc electrode with SiC wafers immersed in an HF solution and application of 3 V to the Pt electrode with respect to a reference Ag electrode. In this method, no bias voltage is necessary to apply to SiC. After polishing for 3 h using the developed method, the surface roughness Ra value of 7.91 nm (500 × 500 nm2 area) for mechanically polished n-type 4H-SiC (000-1) wafers decreases to 0.12 nm (500 × 500 nm2 area) without formation of a damaged layer. From XPS measurements, formation of a ∼0.4 nm thick SiO2 layer is evident on the SiC surface in cases where the solution doesn't contain HF. By application of a DC voltage higher than 2 V to the Pt disc electrode, hydroxyl radicals (OH radicals) are observed by use of a luminescence probe method with tele-phthalic acid. From these results, the following planarization mechanism is concluded: OH radicals having high oxidizing ability are generated on the Pt disc electrode surface during water electrolysis, oxidize SiC to form SiO2, and then, SiO2 is dissolved by the reaction with the HF solution.