Reaction of Si surfaces with a C2H4 beam

The reactions of Si(100) and (111) surfaces with a C2H4 beam in ultrahigh vacuum were studied using high resolution X-ray photoelectron spectroscopy (WS) at temperatures of 600-900 degrees C. These reactions produce silicon carbide (SiC) layers on the silicon surfaces, the growth rates of which increase with surface temperature up to about 675 degrees C, but decrease at higher temperatures. The observed behavior is explained by the balance between the carbon supply rate from the C2H4 beam and the silicon out-diffusion rate from the substrate to the carbide surface. The carbon supply rate is limited by the surface residence time of chemisorbed C2H4 and the beam flux. At the temperature of maximal growth the composition ratio of carbon to silicon in the carbide layer is close to unity, but decreases with increasing temperature. Below the optimal temperature the FWHM of the C Is XPS peak is broader than that of the stoichiometric compound SiC, implying that the chemical bonding in the carbide layer is distributed. The SiC bulk plasmon-loss peaks accompanying the Si 2s and C Is XPS peaks appear in carbide films thicker than about 13 Angstrom.