Surface preparation of 4H–SiC substrates for hot-wall CVD of SiC layers

The properties of an epitaxial grown layer are sensitively dependent on the surface quality of the substrate, since most defects may propagate into the grown epitaxial layer and degrade its quality. The surfaces of mechanically prepared 4H–SiC substrates are characterised by a large number of deep scratches and a subsurface damage layer. Atomic force microscopy (AFM), electron channelling pattern (ECP) technique carried out in a scanning electron microscope (SEM), and high voltage transmission electron microscopy (HVTEM) were used to investigate the surface morphology and the crystalline perfection of the subsurface region. The damage on 4H–SiC(0 0 0 1)8°off wafers caused by mechanical polishing was efficiently removed by a combination of improved mechanical preparation and an etching step with hydrogen/propane gas in a hot-wall chemical vapour deposition (CVD) reactor immediately before the layer deposition. The obtained surface is free of scratches and shows a weak periodic structure like parallel ridges. Cross-sectional HVTEM investigations and ECP studies show no observable subsurface damage.