Shinichi Mukainakano

Reconstructions of 6H-SiC(0001) Surfaces Studied by Scanning Tunneling Microscopy and Reflection High-Energy Electron Diffraction

Surface reconstructions and surface decomposition of 6H-SiC(0001) covered with Si were observed using scanning tunneling microscopy (STM) and reflection high-energy electron diffraction (RHEED). The 3×3 structure terminated with Si atoms was obtained by annealing at 1050°C; this changed to a mixture of the graphite 1×1 and SiC 6×6 by annealing at 1300°C. The graphite 1×1 consisted of two types of graphite lattices, rotated 30° with respect to the SiC lattice and along the SiC lattice. The SiC 6×6 was terminated with C atoms. The RHEED spots due to the double diffraction between the SiC (02) spot and the graphite spot rotated by 30° with respect to the SiC lattice were observed. The thickness of the graphite layer and the area of the graphite region increased by successive annealing. String-shaped structures were formed along the steps at 1450°C. Further annealing up to 1800°C resulted in the formation of a thick graphite layer and amorphous carbon.

Solid-Phase Reactions in Al Alloy/TiN/Ti/Si Systems Observed by In Situ Cross-Sectional TEM

The mechanism of solid-phase reactions for multilayers of Al-1%Si-0.5%Cu/TiN/Ti/n+-Si substrates has been investigated by means of in situ and high-resolution/analytical cross-sectional transmission electron microscopy (X-TEM). We have succeeded for the first time in real-time observation of the instant of barrier breakdown of the TiN layer. An intermediate Al-Ti-Si(-N) layer ( ~4 nm thickness) composed mainly of microcrystallites was formed at the Al alloy/TiN interface at ~450° C, and the microcrystalline phase grew along the TiN grain boundaries. At over ~500° C, the Al diffused downward very rapidly through the TiN layer, forming an Al region under the TiN layer. It is concluded that the rapid redistribution of the Al may be caused by movement along the TiN grain boundaries in the microcrystalline state.

The (3×3)R30° reconstruction on hexagonal 6H–SiC(0001) surface with and without a Si flux

The (√3 x √3)R30° reconstruction on hexagonal 6H-SiC(0001) surface and its properties were studied by using reflection high-energy electron diffraction (RHEED) and RHEED multislice dynamical calculations. A Si coverage of 1/3 monolayer occupying the threefold-symmetric T 4 or H 3 sites develops upon a lower Si flux and/or at a higher annealing temperature and/or upon a longer time annealing. However, Si trimers centered on the T 4 positions with 1 monolayer coverage may be another appropriate candidate for the (√3 × √3)R30° reconstruction obtained under a very Si-rich condition and/or at a lower annealing temperature and/or upon a shorter time annealing.

Structural Study of the SiC(0001)(√3×√3)-R30\degree Surfaces by Reflection High-Energy Electron Diffraction Rocking Curves

Two types of √3×√3 surfaces, silicon-rich and carbon-rich, have been observed in a series of annealing processes. Rocking curves from the surface structures of both √3×√3 surfaces have been analyzed by reflection high-energy electron diffraction (RHEED) dynamical calculations. The silicon-rich √3×√3 surface is determined to be terminated with Si adatoms on T4 or H3 sites of the silicon terminated bulk surface. It is considered that the carbon-rich √3×√3 surface consists of a C honeycomb structure. From the results of Auger spectra and RHEED rocking curves, the phase transition from the silicon-rich to the carbon-rich √3×√3 phases is caused by adsorption of atomic hydrogen on the silicon-rich √3×√3 surface.

Dependence of diffusion barrier properties in microstructure of reactively sputtered TiN films in Al alloy/TiN/Ti/Si system

Abstract We have been investigated the diffusion barrier properties of the reactively sputtered titanium nitride (TiN) in Al1wt%Si0.5wt%Cu/TiN/Ti/Si system. The lower dense but N-rich TiN film was easy to react with the Al, showing the poor diffusion barrier properties. By means of plan-view TEM, lots of disorder regions and vacancies in the TiN film could be observed. We conclude that the rearrangement in the lower dense films is easier to occur by thermal treatment, giving rise to diffusion of Ti atoms, even if the TiN is N-rich film. This conclusion indeed implies the dense degree of the TiN film in atomic level has a significant effect on the reaction between the TiN and the Al, or the diffusion barrier properties.

Atomic models of (∛×∛)R30° reconstruction on hexagonal 6H–SiC(0001) surface

By using reflection high-energy electron diffraction (RHEED) and RHEED multislice dynamical calculations, the atomic structures of the (∛×∛)R30° reconstruction on 6H–SiC(0001) surface were solved. Both the simple adatom structure with a Si coverage of one-third monolayer occupying the threefold-symmetric T4 or H3 sites and a bit complex structure with Si trimers centered on the T4 positions with 1 monolayer coverage are all compatible with our results.

Initial Oxidation of 6H-SiC (0001) (3 x 3)-R30° and 3 x 3 Surfaces Studied by AES and RHEED

Initial oxidation of the SiC (0001) (√3×√3)-R30° and 3×3 surfaces at various temperatures is studied by using Auger electron spectroscopy (AES) and reflection high-energy electron diffraction (RHEED). The results show that the 3×3 surface oxidizes with maintaining its original periodicity, while the √3×√3 surface changes into a 1×1 structure. Moreover, the √3×√3 surface loses almost all Si-Si bonds by a low oxygen exposure, in contrast the 3×3 surface does not. There is no significant difference among the Auger spectra at different sample temperatures in the case of the √3×√3 surface, while thermal activation is found in the 3×3 case at 500°C.

Reconstruction of the 6H–SiC(0001) √3×√3-R30° surfaces by adsorption of hydrogen in ultra high vacuum

Reconstruction of the 6H/SiC(0001)3/3-R308 surfaces in ultra high vacuum (UHV) has been studied by rocking curves of reflection high energy electron diffraction (RHEED) intensities and Auger electron spectroscopy (AES). It is found that the silicon rich 3/3 surface is unstable in UHV. This 3/3 surface transforms into the carbon rich 1/1 surface in rather short time. The phase transition is concluded to be caused by atomic hydrogen adsorbed on the silicon rich surface. Annealing the 1/1 surface leads to the carbon rich 3/3 surface, which transforms into the silicon rich 3/3 surface by successive annealing in UHV. The results show that silicon adatoms on the silicon rich 3/3 surface is not etched by the adsoption of hydrogen but reside on the surface as silicon clusters in the reconstruction process to work as a silicon source in the successive annealing. # 2002 Elsevier Science B.V. All rights reserved.