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 (SiH ₄ ) to propane (C ₃ H ₈ ) 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 (SiO ₂ and SiO _x 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 C ₃ H ₈ source flow, and comprised largely of unreacted C ₃ H ₈ or its intermediate products such as C ₂ H ₂ and C ₂ H ₄ . 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.