Carbonization of Si(111)-7×7 Surface Using CH₄ with Hot Tungsten Filament

The reaction of CH₄ on a Si(111)-7×7 surface is investigated by reflection high-energy electron diffraction (RHEED) analysis, quadrupole mass spectroscopy (QMS) and scanning electron microscopy/energy dispersive analysis of X-ray (SEM/EDAX). The RHEED patterns during CH₄ exposure indicate the evolution of structures such as δ-7×7, 1×1, √3×√3 and SiC for various exposures at temperatures from room temperature (RT) up to approximately 800 °C. A mass spectrum shows that CH₄ decomposition products are primarily CH₃, CH₄, and H₂ at a tungsten filament temperature of 1500 °C. A SEM image of the SiC formed at 825 °C and 7920 L shows that the surface is rugged and consisted of hills and valleys. On the basis of the EDAX measurements, it is determined that the SiC layers are C-rich at the hill and Si-rich at the valley. It is found that the SiC layer is generated only after the formation of the √3×√3 structure.