Si Double Layer Research Articles

Structure determination of the CoSi2(111) surface using medium-energy ion scattering.

The surface structure of epitaxially grown ${\mathrm{CoSi}}_{2}$ crystals on Si(111) has been investigated with use of medium-energy ion scattering. A Co- or a Si-rich surface composition is obtained, depending on the preparation conditions. The structure of the Co-rich surface is shown to be bulklike, i.e., the crystal is terminated by a Si-Co-Si triple layer. The Si-rich surface is found to have, on top of the last Si-Co-Si triple layer, a Si double layer of the same orientation as the ${\mathrm{CoSi}}_{2}$ bulk lattice. This accounts for the difficulty to grow a 180\ifmmode^\circ\else\textdegree\fi{}-rotated Si film on top of ${\mathrm{CoSi}}_{2}$(111) by normal molecular-beam-epitaxy techniques. The topmost Co atoms of the Si-rich surface are eightfold coordinated.

Determination of the SiO_2/Si interface roughness by diffuse reflectance measurements

The problem of determining the roughness of the SiO(2)/Si interface is treated. A model is used based on the Fresnel formalism and scalar scattering theory. The resulting formulas express the diffuse reflectance as a function of the optical constants of the two materials, the oxide thickness and the rms roughness of the interfaces. Using the roughness values as adjustable parameters, quantitative information about the interface roughness is obtained from the diffuse reflectance spectra for an SiO(2)/Si double layer. Excellent agreement between calculated and experimental spectra is obtained for an rms roughness of 9.0 nm at the front surface and 2.2 nm at the oxide substrate interface for the case of a low-pressure low-temperature CVD film of SiO(2) on Si.

Behavior of indium on the Si(111)7×7 surface at low-metal coverage

We have used scanning tunneling microscopy to study the behavior of indium on the Si(111)7×7 surface at low-metal coverages. At sufficiently low densities, In atoms replace Si in the 7×7 adatom positions, preserving the 7×7 structure. In this case the In atoms have a tendency to occupy positions along the edges of the unit cell rather than adjacent to the corner holes. Agglomeration of higher In densities around atomic steps can lead to local areas of √3×√3 reconstruction. Examination of a phase boundary between 7×7 and √3×√3 allows the identification of the bonding site of the In adatoms in the √3×√3 structure as the threefold symmetric site above a second layer Si atom in the surface Si double layer.

Characterization of plasma etching of molybdenum polycid conductor stacks in Cl2/CF4 and Cl2/CF4/O2

AbstractThe present paper is concerned with an extremly anisotropic two‐step patterning process for Mo2Si/poly‐Si double layers with an etch‐stop on thick P‐doped CVD‐SiO2. As etching gas Cl2/CF4/O2 and Cl2/CF4 are used. By means of etch rate dependencies, volatilities of possible reaction products and results, obtained from the literature it is attempted to develop a simple qualitative model on the chemism of the process.

Scanning tunneling microscopy on Si(112)

Using scanning tunneling microscopy (STM) we have measured a macroscopic Si(112) surface. A large part of the surface consisted of narrow (111) terraces with a step height corresponding to a Si double layer. Projected into the [112] direction the surface showed rows of atomic features, which are orientated along the [110] direction. We identified neighboring atoms at a distance in agreement with the ideal Si lattice, adatoms and holes with twice this distance corresponding to a local reconstruction along the rows and triangular arrangements of atoms. The separation between the rows only in some cases agreed with that of a microscopic Si(112) surface. This fact and the frequent observation of 7×7 reconstructed Si(111) facets do not indicate a large stability of Si(112).

The Effect of Surface Structure on the Epitaxial Growth of Si on CoSi2(111)

ABSTRACTTwo distinctively different structures were found on CoSi2(111), the CoSi2-C and the CoSi2-S, which correspond to, respectively, an essentially bulk-terminated surface and one which consists of an additional Si double layer. Details of the two structures suggest new growth techniques for Si epitaxy. Single crystal Si layers with either identical orientation as the silicide or a 180°-rotated orientation can be fabricated by use of carefully designed Si templates.