Effect of kinetic and vibrational energy of molecular beam on surfase reactions

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For study of reaction mechanisms of gaseous molecule and solid surface, we have constructed a new molecular beam apparatus which is attached to a multi-surface analysis system. In the present work, carbonization and nitridation of Si surface have been investigated.For the carbonization an ethylene beam was irradiated on the clean and heated Si surfaces. After the reaction the surfaces were analyzed by low energy electron differaction (LEED) and X-ray photoelectron spectroscopy (XPS). The reaction occured above 600ﾟC.The reaction rate increacsed with temperature up to 675ﾟC,but it decreased above the temperature. In an initial stage of the reaction a change of the LEED patern was observed, which means that the deposited C atoms were regularly arranged on the Si (100) surface. The reactive C and Si atoms were supplied on the growing carbide layr by the ethlene beam and the outdiffusion of Si atoms in the substrate, respectively. At the lower temperatures than 675ﾟC the outdiffusion of Si is the rate-determining step of the carbide layr growth. At the higher temperatures, the rate of the C supply is the rate determing step. The C supply rate may decrease with the temperatre due to the residence time the carbide layr was nearly unity at 675ﾟC,which suggests that the both supplies were balanced at the temperature.For the nitridation we have used a N_2^+ ion beam of energy between 100 and 1000eV.The chemical change of the surface layr during the beam irradiation was studied by XPS.At the lower energies of 100-200eV a very thin film of a nearly stoichimetric compound Si_3N_4 was formed, but at the higher energies the nitride layrs contained many defects. The defects were partially dimished by annealing.