Surface chemical states on LPCVD-grown 4H-SiC epilayers

A series of 4H-silicon carbide (SiC) epilayers grown on 4H-SiC substrates by low pressure chemical vapor deposition (LPCVD) with different silane (SiH4) to propane (C3H8) gas flow ratios were studied by angle resolved X-ray photoelectron spectroscopy (ARXPS) and atomic force microscopy (AFM). ARXPS revealed that the surfaces of the samples consisted of elemental Si, Si oxides (SiO2 and SiOx where x<2) and unreacted C-H species, in addition to the stoichiometric SiC compound. Small amounts of elemental Si were also detected within the 4H-SiC epilayers. The surface thickness of the C-H overlayer showed a positive correlation with the C3H8 source flow, and comprised largely of unreacted C3H8 or its intermediate products such as C2H2 and C2H2. This C-H overlayer had an rms roughness of 0.4 +/- 0.1 nm as determined by AFM. The roughness was independent of the Si:C source ratio. AFM analyses revealed numerous micro-scratches which were the polishing marks on the 4H-SiC substrate copied by the epilayers. (C) 1998 Elsevier Science B.V.