Ayahiko Ichimiya

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.

Reaction of Si(111) Surface with Saturated Hydrocarbon

Reaction of Si(111) surface with saturated hydrocarbon such as methane (CH4) and ethane (C2H6) was carried out in a gas source molecular beam epitaxy (GSMBE). After carbonization, structures formed on the surface were observed by in situ reflection high‐energy electron diffraction (RHEED). Structures transition formed on the surface were 7×7, δ‐7×7, 1×1, and SiC structures. In the case of CH4, the Si surfaces were carbonized at 800 °C for 120 min (7.2×104 L) with a W‐filament of 2800 °C, and SiC layers were obtained. In the case of C2H6, the mixture of 7×7 and SiC structure was observed. Decomposition of hydrocarbon was characterized in quadrupole mass spectroscopy (QMS) measurements. An atomic force microscopy (AFM) image of the mixture of 7×7 and SiC shows a wandering shape. Whereas, the SiC layer shows a regular step. This result seems to be related to the different in the amount of CH3 molecules on the surface.