AVS 51st International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP5
Irradiation Effects of Undulator Synchrotron Radiation Beam on Hydrogen-Terminated Si (111) Surfaces Studied by STM

Tuesday, November 16, 2004, 4:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: Y. Nonogaki, Institute for Molecular Science, Japan
Authors: Y. Nonogaki, Institute for Molecular Science, Japan
T. Urisu, Institute for Molecular Science, Japan
Correspondent: Click to Email
Undulator synchrotron radiation (USR) is a powerful light source for observation of surface VUV-photochemical reactions, since it is quasi-monochromatic and has high photon flux. It is also very attractive for semiconductor device processes using photochemical reaction. We have designed and constructed a beamline for surface photochemistry and nanofabrication of semiconductor at the UVSOR facility. Using this beamline hydrogen desorption on hydrogen-terminated Si (111) surfaces (H-Si (111)) was investigated using the USR and STM observation. We successfully observed that H-Si (111) was drastically changed after the USR irradiation. H-Si (111) was prepared with atomic H exposure to Si (111) 7x7 at surface temperature of 350°C for 10 min. The H-Si (111) was exposed to the USR at room temperature for 5 to 60 sec, where 1st harmonic of the USR was centered at 100 eV. Correspondent irradiation dose is 1000 to 10000 mAsec (ring current x time). STM observation was performed with tungsten tips at room temperature. STM observation of H-Si (111) showed that there were adatom islands and small protrusions on rest-atom monohydride surface. The adatom islands have triangular shape and bilayer height typically, of which coverage was ~15%ML. On the rest-atom monohydride surface, extension of unfaulted regions were observed and faulted regions was ~20%ML. Surface morphology was changed after USR irradiation. Density of the small protrusions significantly increased with irradiation dose from 1.4%ML at 0 mAsec to 12.8%ML at 10000 mAsec. The distribution of small protrusions were random whether on unfaulted and faulted region. The rest-atom monohydride surface seems to be unchanged. The small protrusions are assigned to dangling bond formed by irradiation-stimulated H-desorption from the rest-atom monohydride on the surface.