AVS 49th International Symposium
    Nanometer Structures Wednesday Sessions
       Session NS-WeM

Paper NS-WeM3
Selective Oxidation of Faulted Halves of Si(111): (7x7) with Ozone

Wednesday, November 6, 2002, 9:00 am, Room C-207

Session: Nanostructured Materials
Presenter: K. Miki, NRI-AIST and NIMS, Japan
Authors: K. Miki, NRI-AIST and NIMS, Japan
T. Narushima, NRI-AIST, Japan
M. Kitajima, NIMS, Japan
Correspondent: Click to Email
For nano-scale devices, an electronic isolation technique is desired since the working current is very small and therefore leakage through the substrate should be suppressed. In this paper we demonstrate a nano-scale selective reaction to realize this isolation technique. For this model case, we used an ozone radical to selectively oxidize one subunit of Si(111)-7x7. This surface has two different subunits; the faulted and unfaulted halves. Due to whether or not a stacking fault exists, the electronic states of the two halves differ, especially around 0.5 eV below Ef. This state is the backbond state of the adatoms. Therefore we could expect selective oxidation with some radicals on either the faulted or the unfaulted half. In conventional thermal oxidation, this possibility has already been denied, while ozone remains a possibility. We introduced highly concentrated ozone gas onto 7x7 reconstructed Si(111) surface in a UHV chamber in a split second. At room temperature, by means of scanning tunneling microscopy, it is found that the faulted sites are imaged as depressions at the sample bias of 0.8 V, but the other sites are mostly unchanged. This depression could be due to back bond oxidation. The reactive site of the oxygen changed with temperature, up to 873 K. As the substrate temperature increased, the chemical reaction selectivity disappeared. This may be due to diffusion of backbond oxygen atoms, which has a barrier height around 1eV. We intend to make 2.7 nm-size nano structure (unit size of 7x7) with atomic scale isolation of backbond oxidation state. It is very useful because it does not involve processing at high temperature, which could induce damage, or disappearance, of nano structures.