Initial Oxidation of Si(001) Induced by the Translational Kinetic Energy of O2 Supersonic Molecular Beams

Abstract

The influence of the variation of up to 3.0 eV in the incident translational kinetic energy of O2 (Et) on the chemisorption of O2 onto Si(001) surfaces was studied by using the supersonic molecular beam (SSMB), X-ray photoemission spectroscopy (XPS), O2 molecular scattering and desorbed SiO detection techniques. Under passive oxidation conditions at room temperature, the amount of saturated oxygen on the Si(001) surface was enhanced in concomitant with an increase in the translational kinetic energy of O2. Threshold energies, corresponding to potential energy barriers for the direct oxidation reaction, are clearly observed at Et=1.0 eV and Et=2.6 eV. These threshold energies have been assigned to backbond oxidation of the Si dimer atoms and oxidation between the second and the third Si layers, respectively. Futhermore, at substrate temperature of 700°C, the relative desorption rate of SiO was increased when the translational kinetic energy of O2 was greater than Et=1.0 eV. These results suggest that the oxidized Si dimer backbond is the precursor for the desorbed SiO.