PREPARATION OF ATOMICALLY FLAT SURFACES ON SILICON-CARBIDE USING HYDROGEN ETCHING

Hydrogen etching of 6H- and 4H-SiC(0001) surfaces is studied. The as-p olished substrates contain a large number of scratches arising from th e polishing process which are eliminated by hydrogen etching. Etching is carried out in a flow of hydrogen gas at atmospheric pressure and t emperatures around 1600-1700 degrees C attained on a tantalum strip he ater. Post-etching atomic force microscopy images show periodic arrays of atomically flat terraces that are a few thousand angstroms wide. T hese terraces are separated by steps 15 Angstrom high in the < 1 (1) o ver bar 00 > directions. Often, the surface is seen to be faceted with steps on neighboring facets forming 60 degrees angles and offset in t he c-direction by half a unit cell. Images of incompletely etched surf aces show early stages of etching where one can see remnants of surfac e damage in the form of arrays of hexagonal pits. On the larger scale, the surface has a hill-and-valley type morphology. The observed featu res are interpreted in a model based on the symmetry of the SiC unit c ell and crystal miscut.