AVS 53rd International Symposium
    Applied Surface Science Friday Sessions
       Session AS-FrM

Paper AS-FrM1
Probing Interactions of Ge with Chemical and Thermal SiO@sub 2@ to Understand Selective Growth of Ge on Si during Molecular Beam Epitaxy

Friday, November 17, 2006, 8:00 am, Room 2005

Session: Thin Film Characterization
Presenter: Q. Li, University of New Mexico
Authors: Q. Li, University of New Mexico
J.L. Krauss, University of Wisconsin Madison
S. Hersee, University of New Mexico
S.M. Han, University of New Mexico
Correspondent: Click to Email
We have previously demonstrated that Ge selectively grows on Si over a SiO@sub 2@ mask during molecular beam epitaxy. We have also demonstrated that epitaxial Ge rings selectively form at the contact region between chemical-oxide-covered Si and self-assembled SiO@sub 2@ sphere. In order to determine the surface phenomena responsible for the selectivity, we probed the interactions of Ge with 1.2-nm-thick chemical SiO@sub 2@ films and 6 to 200-nm-thick dry thermal SiO@sub 2@ films grown on Si(100). The change in Si2p x-ray photoelectron intensity and position, intermittently measured during the Ge beam exposure, reveals that the chemical oxide degrades at substrate temperatures near 600°C. In contrast, the change in thickness and surface roughness of the thermal oxide, measured by ellipsometry and atomic force microscopy, is below the detection limit after a prolonged Ge exposure at temperatures below 700°C. For thermal SiO@sub 2@, where oxide degradation is not observed, we have determined that the selectivity stems from the low desorption activation energy (E@sub des@) of Ge adspecies from the thermal SiO@sub 2@ surface. The experimentally measured E@sub des@ is 42±3 kJ/mol. The low E@sub des@ entails a low activation barrier (~13 kJ/mol) for surface diffusion. We expect the large diffusion length on the order of 1 µm to cause Ge adspecies to migrate over SiO@sub 2@ and preferentially aggregate on exposed Si surface. In order to determine the identity of stable Ge adspecies on SiO@sub 2@, the nucleation of Ge on thermal SiO@sub 2@ surface is also studied by plan-view, high-resolution scanning electron microscopy at substrate temperatures ranging from 300 to 500°C. We have found that the saturation Ge island density is a strong function of substrate temperature, but a weak function of absolute Ge flux. This result suggests that Ge monomers can exist as a stable nucleus on thermal SiO@sub 2@.