The purpose of this work is to clarify the sources of carbonaceous (C-) contamination on hydrogen(H)-passivated Si surface before an epitaxial growth. The dependence of C-contamination on the residence time in the loading chamber, $t_{LC}$, was investigated with or without operating a vaxuum ion gauge. The results indicated that C-contamination of H-passivated surface greatly increased by the ion gauge operation in the loading chamber. The presence of C-contaminant could be determined by observing SiC diffraction pattenrs using in situ-reflection high energy electron diffraction. The C-contaminants reacted with Si to produce single crystalline SiC at a temperature as high as 85$0^{circ}C$. The microstructure and the distribution of SiC were studied using the cross-sectional high resolution transmission electron microscopy. As the C-contamination increases, the reaction increases the thickness of SiC islands rather than to increase the coverage of SiC over Si during the thermal treatment. In the following epitaxial growth of Si, well oriented single crystalline Si layer could be grown over the SiC island. Longer $t_{LC}$ with operating ion gauge also require higher temperature to achieve to achieve 2xl reconstructed structure from H-passivated Si surface.