Structure and morphology of 4H-SiC wafer surfaces after H2-Etching

Commercial on-axis wafers of 4H-SiC(0001) were etched in a standard reactor for chemical vapor deposition (CVD) using molecular hydrogen flux in order to improve the structure and morphology of the surface. The substrate temperature during etching was varied from 1400 to 1600 degrees C. Characterization of the surface morphology was performed using optical and atomic force microscopy (AFM). Low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS) were also used to examine the surface structure and chemical composition of the samples. The sample of best quality was obtained for an etching temperature of 1400 degrees C. Its surface is (root 3x root 3)R30 degrees reconstructed and covered by an ordered "silicate" layer. Increasing the substrate temperature during etching to 1500 degrees C leads to enhanced step-bunching and the formation of macro-terraces. At 1600 degrees C distinct depressions appear on the surface, presumably from etching of structural defects such as screw dislocations. Subsequent annealing at 1000 degrees C in ultra-high vacuum (UHV) removes the surface oxide and produces the (root 3x root 3)R30 degrees surface phase of clean 4H-Sic(0001).