SiC film formation and growth by the thermal reaction of a film adsorbed on a Si(111)-(7) surface: Bonding nature of molecules and SiC-film surface phonons

We report here measurements of temperature-dependent vibrational excitations of (Formula presented) molecules adsorbed on a Si(111)-(7(Formula presented)7) surface, and the formation of a SiC film by thermal reaction using high-resolution electron-energy-loss spectroscopy (HREELS). The interactions of (Formula presented) molecules with the Si surface are judged from the charge states of (Formula presented) molecules, determined quantitatively by the energy shifts of the vibrational modes. Most (Formula presented) molecules interact weakly by van der Waals force at room temperature. At 670 K, two adsorption states, i.e., ionic and covalent bonds, are formed under the rearrangement of surface Si atoms. The amount of charge transfer is estimated to be (4(Formula presented)1) electrons per (Formula presented) molecule for the ionic bond. At 1070 K, covalent bonds between (Formula presented) molecules are formed, and at 1170 K (Formula presented)-SiC(111) islands are formed. The formation of (Formula presented)-SiC(111) is verified by the observation of the surface-optical-phonon Fuchs-Kliewer mode. We have grown the (Formula presented)-SiC(111) film, repeating the adsorption of (Formula presented) molecules, and annealing the sample. Well-oriented films with low step density are obtained. The lower-energy shift of the Fuchs-Kliewer mode, observed for (Formula presented)-SiC(111) films thinner than 30 nm, indicates the softening of the Si-C bond caused by the buffer layer.