AVS 52nd International Symposium
    Surface Science Wednesday Sessions
       Session SS1-WeA

Paper SS1-WeA7
Surface Morphologies produced by Oxygen Etching of Stable and Unstable Si Surfaces

Wednesday, November 2, 2005, 4:00 pm, Room 200

Session: Surface Structure and Morphology Modification
Presenter: A.A. Baski, Virginia Commonwealth University
Authors: A.A. Baski, Virginia Commonwealth University
M.L. Willis, Virginia Commonwealth University
J.W. Dickinson, Virginia Commonwealth University
J.L. Skrobiszewski, Virginia Commonwealth University
Correspondent: Click to Email
We have used scanning tunneling microscopy (STM) and atomic force microscopy (AFM) to study the morphologies produced on Si surfaces by oxygen etching. When Si surfaces are heated to between 700 and 850°C and exposed to O@sub 2@, the simultaneous processes of etching and oxide nucleation can significantly modify the surface structure. As etching removes surface atoms, oxide-induced pinning sites can modify the step structure and lower-energy facet planes can be exposed. In these experiments, a range of O@sub 2@ exposures (50 to 400 L) have been explored for surface orientations that include: (001), (111), (113), (5 5 12), and (112). All of these orientations except Si(112) form stable, clean surface reconstructions. At lower exposures and temperatures, oxygen etching on all of the surface orientations leads to step retraction and the appearance of islands on terraces and at step edges. These islands are presumably due to oxide-induced pinning sites that remain as the surrounding area is etched. The high-index (113) and (5 5 12) surfaces show significantly less terrace etching and enhanced island nucleation along step edges. At higher exposures and temperatures, fewer kinetic limitations are present and the resulting morphologies reflect the stability of surface planes. The (001), (111), and (113) surfaces remain relatively flat with monolayer islands that reflect the surface symmetry. In contrast, the less thermodynamically stable (5 5 12) surface is etched to expose linear sawtooth structures composed of (111) and (113) planes. Similarly, the unstable (112) surface shows dramatic restructuring with the formation of sawtooths composed of (111), (113), (225), and/or (337) planes. Short (112) segments are also sometimes observed, indicating that adsorbed oxygen may stabilize this otherwise unstable orientation. Further studies are in progress to examine exposures above 1000 L where a steady-state morphology should exist.