S. Teichert

Surfactant mediated growth of MnSi1.7 on Si(001)

Sb is used as a surfactant for the growth of MnSi1.7 by reactive deposition of Mn on Si(001). It is found that the presence of Sb during the growth strongly increases the island density and changes the crystalline orientation of the MnSi1.7. The morphology and structure of the resulting silicide are the same both for the deposition of Mn only on a Sb-terminated Si(001) surface and for the codeposition of Mn and Sb on Si(001). A residual Sb coverage close to one monolayer at the sample surface has been determined for both of the preparation conditions.

Real structure of the CoSi2∕Si(001) interface studied by dedicated aberration-corrected scanning transmission electron microscopy

The interface structure of epitaxial cobalt disilicide thin films buried in (001) silicon was studied by dedicated aberration-corrected scanning transmission electron microscopy. Two different CoSi2∕Si interface structures, one representing a (2×1) reconstruction containing sevenfold coordinated Co and the other, a (1×1) structure containing eightfold coordinated Co, were unequivocally identified. The reconstructed sevenfold interface structure was observed more frequently than the (1×1) eightfold interface, which confirms first-principles total-energy calculations. Further, the atomic arrangement found in the eightfold interface reveals an atomic displacement, which is due to relaxation and has been predicted theoretically as well. Complex defect structures at interface domain boundaries are described.

Preparation and properties of MnSi 1.7 on Si(001)

Abstract The most rich silicon silicides of manganese, the group of higher manganese silicides (HMS), have the composition MnSix with x in the range from 1.67 to 1.75. This material group with a tetragonal crystal structure shows semiconducting electronic properties, with promising application in thermoelectric devices. This paper reports the structural and morphological properties of HMS prepared by a reactive deposition process on Si(001) under UHV conditions. X-ray diffraction shows, for all samples grown at substrate temperatures ranging from 400 to 750°C, the growth of HMS only. Scanning electron microscopy and Rutherford backscattering spectrometry show a transition from film growth to island growth with increasing substrate temperature. A detailed analysis of the XRD spectra shows a change of the texture of HMS at the transition of the sample morphology. The results are discussed on the basis of anisotropic growth rates for differently oriented grains of HMS.

Electron microscopic investigation of MnSi 1.7 layers on Si(001)

Semiconducting higher manganese silicides (HMS) with a composition near that of MnSi1.7 are of special interest due to their thermoelectric properties. We report on the growth of HMS layers deposited by MBE using the template technique. In particular the influence of the template thickness on the structure and morphology of MnSi1.7 films on (001)Si substrates was investigated. It was found that there is an optimal template thickness that causes preferred epitaxial growth of the major amount of the silicide. Three different epitaxial orientation relations of the silicide crystals to the substrate were observed. Considering the specific features of the electron diffraction patterns of MnSi1.7 the HMS phase was identified as Mn4Si7.

The growth of an intermediate CoSi phase during the formation of epitaxial CoSi2 by solid phase reaction

Abstract Among the epitaxial transition metal silicides CoSi 2 is of special interest for applications in ULSI technology due to its high thermal stability and low electrical resistivity. The solid phase reaction of metallic bilayers with Si in an N 2 ambient is a well-known process for growing epitaxial CoSi 2 . However, the real function of the so-called diffusion barrier, which is arising during the annealing process, remains unclear. TEM studies revealed the intermediate growth of a CoSi phase with grains of preferred orientation to Si. The growth of this phase raises the temperature of CoSi 2 nucleation, which starts at the CoSi/Si interface. The nucleation temperature determines the quality of the growing epitaxial CoSi 2 , which is better for Ti as a barrier forming material than for Hf, also used successfully. Whether an intermediate oriented growth of CoSi is promoting the epitaxial quality of CoSi 2 otherwise than by shifting the nucleation temperature, remains an open question.

Epitaxial CoSi 2 by solid phase reaction of Co/Ti and Co/Hf bilayers on Si(001)

Abstract TEM and RBS studies of the solid phase reaction of Co/Ti- and Co/Hf/Si(001) layer systems are reported. In addition to conventional annealing procedures a special thermal treatment was applied to investigate the intermediate stages of the reaction during heating up. With rising temperature a complex Co–Si-phase sequence was observed which finally results in the growth of epitaxial CoSi 2 . The emerging silicide phases were proved to grow with preferred orientation relations to the substrate. The observed growth behaviour is compared for both the systems and discussed considering aspects of energy minimization and material supply under the conditions of a thin film reaction.

Surfactant mediated growth of MnSi 1.7 layers on (001) Si

This study reports on transmission electron microscopy investigations of higher manganese silicide (HMS) layers grown by molecular beam epitaxy (MBE) on (001)Si using the surfactant mediated reactive deposition technique. Applying Sb as a surfactant (surface active substances) results in an increased silicide island density as well as in a change in the crystalline orientation of the silicide islands. The silicide islands were found to grow into the Si matrix. The preferential epitaxial relationship was determined to be (100)[010]Mn4Si7 || (001)[100]Si or (010)[??00]Mn4Si7 || (001)[100]Si. In [100]Si cross-sectional view the silicide crystallites of this orientation appear with a smooth Mn4Si7/(010)Si interface and a slightly inclined to (001)Si Mn4Si7/Si interface, which is suggested to split up into two local sections: Mn4Si7/(001)Si and Mn4Si7/(011)Si.

Structure, interface roughness, and growth mechanism of reactive deposition epitaxy of CoSi2 on Si(100) substrates

Thin CoSi2 films have been grown on Si(100) substrates using the relative deposition epitaxy method. The structure of the silicide films have been analyzed using x-ray diffraction, transmission electron microscopy (TEM), and Rutherford backscattering spectrometry and channeling, and the interface roughness of the CoSi2/Si(100) is analyzed using specular x-ray reflectivity and cross-sectional TEM. The structure and interface roughness of CoSi2/Si(100) is found to be dependent on the substrate temperature. Highly epitaxial CoSi2 with minimum interface roughness is obtained when the film is grown at substrate temperatures around 900 K. The observed interface roughness is a parabolic function of temperature. The achievement of the best silicide at a substrate temperature around 900 K is explained on the basis of the instantaneous diffusion of Co through growing CoSi2.

Surfactant mediated growth of silicides

The surfactant mediated growth of several silicides is reported. The preparation of MnSi1.7, TiSi2 and NiSi2 was carried out by reactive deposition of the metals onto Si(001) and onto Sb terminated Si(001) at substrate temperatures between 400 and 600°C. In case of MnSi1.7, the application of Sb as surfactant strongly increased the silicide island density. In case of TiSi2, a suppression of pinhole formation due to the surfactant was observed. For NiSi2 an enhanced diffusion of Ni was found with respect to the not terminated Si(001) substrate resulting in the formation of larger silicide islands. During the silicide growth process the Sb used for the termination of the Si substrate segregates to the surface of the samples. No remarkable desorption or incorporation of Sb is observed for all the investigated silicides.

Role of a buried ultrathin amorphous interlayer on the growth of Co films on different metal substrates

Thin films of different metals M (M=Ti, Zr, Hf, Nb, Fe, and Ni) of thickness around 10 nm are deposited on Si(100) substrates and a ∼30 nm Co film is deposited on these metal films using the magnetron sputtering method. Cross-sectional transmission electron microscopy (XTEM) shows the presence of a ∼2 nm buried ultrathin amorphous interlayer at the interface between the Co layer and the M layers (M=Ti, Zr, Hf, and Nb). X-ray reflectivity is used to determine the electron density of this buried ultrathin amorphous interlayer. X-ray diffraction (XRD) is used to determine the crystalline quality of the deposited Co film on these various metal film substrates. The XRD peaks of Co(111) and Co(222) are observed when Ti, Zr, Hf, and Nb are used as substrates. Pole figure measurements confirm that the Co film is highly textured on such metallic substrates. On the other hand no characteristic XRD peaks of cobalt are observed when Ni and Fe are used as the substrate, however, XTEM shows the presence of the Co film ...