Preparation of atomically flat surfaces on silicon carbide using hydrogen etching

Hydrogen etching of 6H- and 4H-SiC(0001) surfaces is studied. The as-polished substrates contain a large number of scratches arising from the polishing process which are eliminated by hydrogen etching. Etching is carried out in a flow of hydrogen gas at atmospheric pressure and temperatures around 1600–1700°C attained on a tantalum strip heater. Post-etching atomic force microscopy images show periodic arrays of atomically flat terraces that are a few thousand angstroms wide. These terraces are separated by steps 15 Å high in the 〈1 $ < 1bar 100 > $ 00〉 directions. Often, the surface is seen to be faceted with steps on neighboring facets forming 60° angles and offset in the c-direction by half a unit cell. Images of incompletely etched surfaces show early stages of etching where one can see remnants of surface damage in the form of arrays of hexagonal pits. On the larger scale, the surface has a hill-and-valley type morphology. The observed features are interpreted in a model based on the symmetry of the SiC unit cell and crystal miscut.