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  • 1990-1994  (12)
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  • 1
    Electronic Resource
    Electronic Resource
    Removal of the process-induced fluorine associated to chemical vapor deposition of tungsten onto a polycrystalline silicon gate structure by heat treatment in a hydrogen-containing atmosphere (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2112-2120 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tungsten was deposited from a gas mixture of hydrogen and tungsten hexafluoride onto a polycrystalline silicon gate structure in a chemical vapor deposition system. During the deposition process fluorine was also deposited as an undesired impurity. In order to remove the fluorine, heat treatments in the temperature range 550–1050 °C were performed in a hydrogen atmosphere. By this treatment it is possible to form volatile hydrofluoric acid and hence remove fluorine from the structure. Nuclear-resonance-broadening technique and secondary ion mass spectrometry were used for the analysis of fluorine. Fluorine was detected in all the samples except for the sample heat treated at 1050 °C. Moreover, etching of the polycrystalline silicon was observed. The gettering of fluorine, the etching of silicon and the observed formation of tungsten disilicide at 650 °C are discussed with respect to conceivable mechanisms. A thermodynamic study supporting the interpretations is also included.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346566
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  • 2
    Electronic Resource
    Electronic Resource
    The dominant diffusing species and initial phase formation in Al-Cu, Mg-Cu, and Mg-Ni systems (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4036-4040 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dominant diffusion species in the formation of Al2Cu, Mg2Cu, and Mg2Ni have been determined. These compounds, rich in the lower melting point elements, are the first phases formed in metal/metal binary reactions. It is quite surprising to find that in all three systems, the minority elements, i.e., Cu or Ni, are the dominant diffusing species. This is in marked difference with results obtained in many metal/metal and metal/Si systems, where the dominant diffusion species are usually the majority elements in the initially formed compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352258
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  • 3
    Electronic Resource
    Electronic Resource
    Oxidation and formation mechanisms in disilicides: VSi2 and CrSi2, inert marker experiments and interpretation (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 6213-6223 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The process of atomic transport in the silicide during oxidation of silicide layers formed on Si substrates has been analyzed by means of implanted inert markers. The results confirm that CrSi2 oxidizes via the diffusion of Cr atoms towards the Si substrate, and reveal that the same type of transport occurs in VSi2, which is in opposition to the growth of these disilicides that proceeds via Si motion. Moreover during the oxidation of both VSi2 and CrSi2, the diffusing metal atoms are accompanied by a large proportion of the Si atoms from the silicide which also diffuse towards the substrate. Thus, the experimental evidence now available reveals that all the silicon-rich silicides, in increasing atomic numbers from TiSi2 to NiSi2, oxidize with the formation of metal-free SiO2 in a process that involves the diffusion of both metal and Si regardless of the predominant moving species during silicide formation. In CrSi2, VSi2, as well as TiSi2, with similar structures, examination of the structure shows that diffusion should occur via a vacancy mechanism. The thermodynamic conditions that prevail during oxidation lead indifferently to metal diffusion in one direction or Si diffusion in the other. Any selection between one mechanism or the other has to be dictated by kinetic conditions relating to the relative mobilities of the two atomic species. What is known about this is discussed in detail. Finally it is proposed that the observed dual, parallel diffusion of metal and Si, results from the very nature of the oxidation process which modifies the chemical potential of the atoms at the surface being oxidized. Thus is created a force that drives some of the atoms away from the surface, into the inside of the samples. The best known example of this behavior is the often observed "injection'' of interstitials during Si oxidation, but a similar process is at work in silicide oxidation, with somewhat similar results. Volume effects, thought to play an important role in solid state chemical reactions, are remarkably well illustrated by the oxidation of silicides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346913
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  • 4
    Electronic Resource
    Electronic Resource
    Stability of C49 and C54 phases of TiSi2 under ion bombardment (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2660-2666 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transformation of C49 phase TiSi2 to the low resistivity C54 phase is necessary for many microelectronic applications. Here, we report on attempts to decrease this transformation temperature by low-energy ion bombardment at elevated temperature. Ion irradiation was performed using a broad beam Kaufman ion source operated in N2 or Ar gas between 0.1 and 2 keV beam energy, with ion doses ranging from 2.0×1016 to 1.9×1018 ions/cm2, and sample temperatures from 480 °C to 735 °C. For comparison, room-temperature Ar+ implantation at higher energy (105–210 keV) was performed with a dose of 1016 ions/cm2 with projected ranges within and beyond the TiSi2 layer thickness. Resistivity measurements as a function of temperature, x-ray diffraction, and Rutherford backscattering spectrometry were used to determine the composition and phases. Results show that low-energy ion bombardment does not promote the C49-C54 transformation at the temperatures studied, while ion implantation actually raises the temperature for the transformation. In addition, bombardment of C54 TiSi2 does not cause it to revert to the C49 phase, indicating that both phases appear to be surprisingly stable under ion bombardment. Simulations of defect production using the trim code indicate the formation of a higher number of displaced atoms than are usually required to initiate a transformation. We conclude that the defects introduced into C49 TiSi2 by ion bombardment at energies up to 2 keV are either not sufficient to nucleate the C54 phase or they are annealed out too quickly at the temperature needed for C54 phase growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349380
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  • 5
    Electronic Resource
    Electronic Resource
    Oxidation of titanium, manganese, iron, and niobium silicides: Marker experiments (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5133-5139 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanism of atomic transport inside the silicide during thermal oxidation of silicide layers on Si substrates has been analyzed by means of inert gas markers implanted in TiSi2, Mn11Si19, FeSi2, and NbSi2. Oxidation was carried out in dry oxygen. The marker displacement reveals that the growth of metal-free SiO2 over the first three of these compounds occurs via the reverse motion of metal atoms, from the silicide/oxide to the silicon/silicide interface, rather than through the direct diffusion of Si atoms from the substrate to the oxide. Moreover, analysis of the marker position indicates that the total amount of Si between the marker and the free surface decreases during oxidation, as had been previously observed in the oxidation of NiSi2, CoSi2, and CrSi2. Although this could occur via the formation and evaporation of SiO, it is believed that the loss of Si is due to the motion of Si atoms, also in the "reverse'' direction as for the metal atoms, across the silicide layer. The experiment conducted with NbSi2 shows that this silicide oxidizes via the direct motion of Si from the substrate to the oxide as anticipated. With TiSi2 the initial state of oxidation occurs as described, but the experimental observations imply that thick oxide layers grow via the direct motion of Si from the substrate to the oxide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347053
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  • 6
    Electronic Resource
    Electronic Resource
    Diffusion versus oxidation rates in silicon-germanium alloys (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 78-80 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the oxidation of SiGe alloys of different compositions (between 25 and 75 at.% Ge). All of the oxidations were performed at 900 °C in wet atmosphere on 7500-A(ring)-thick films grown by molecular beam epitaxy. Below 50 at.% Ge, the oxidation remains similar to what has been described previously, i.e., initially, the rate is enhanced by the presence of Ge, the oxide formed is pure SiO2 and a Ge pileup forms at the SiO2/Si-Ge interface. In these relatively thick films, we propose that after extended oxidation, the decrease of Si concentration at the interface slows down oxidation rates enough so that eventually, the oxide thickness for the SiGe alloys ends up smaller than that of pure Si. For alloys containing above 50 at.% Ge, a markedly different behavior is found: A two-layer oxide is formed, consisting of a mixed (Si,Ge) O2 layer near the surface, and a pure SiO2 layer underneath. The rates of oxidation in this case are even faster, since both Ge and Si are being oxidized. The general behavior is explained in terms of the balance of Si and Ge diffusion fluxes, to and from the interface, needed to sustain oxidation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105528
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  • 7
    Electronic Resource
    Electronic Resource
    Room-temperature oxidation of silicon catalyzed by Cu3Si (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2519-2521 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate remarkably rapid oxidation of (100) silicon at room temperature catalyzed by the presence of Cu3Si. Thermal oxidation of Si is normally carried out at temperatures above 700 °C. Oxidation of many metal silicides occurs more rapidly than that of Si, but under controlled conditions results in a surface layer of SiO2. In contrast, the oxidation process described here produces a thick layer of SiO2 underneath the copper-rich surface layer. The SiO2 layer grows spontaneously to over 1 μm in thickness in several weeks in air at room temperature. Analysis by Rutherford backscattering, Auger electron spectroscopy, cross-sectional transmission electron microscopy, and scanning electron microscopy reveals the presence of Cu3Si at the buried SiO2/Si interface, epitaxially related to the underlying Si substrate. Catalytic action by this silicide phase appears responsible for the unusual oxidation process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103260
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  • 8
    Electronic Resource
    Electronic Resource
    Formation of a C49 TiGe2 phase during annealing a coevaporated Ti0.33Ge0.67 alloy (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 3435-3437 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The coevaporated, amorphous Ti0.33Ge0.67 alloy crystallizes at 315 °C into a metastable C49 structure, which transforms to the equilibrium C54 structure at higher temperatures around 535 °C. This result differs from that obtained from binary reactions between Ti and Ge where the C49 phase is not observed. The electron diffraction pattern for the C49 phase exhibits extra spots as predicted by Bourret et al. for a large period polytype [A. Bourret, F. M. d'Heurle, F. K. LeGoues, and A. Charai, J. Appl. Phys. 67, 241 (1990)]. Additional evidence for the formation of the C49 TiGe2 is found by annealing a Ti0.33Ge0.67/Ti0.33Si0.67 bilayer. The bilayer crystallizes into a solid solution of C49 TiGe2-TiSi2 before transforming to a C54 solid solution at lower temperatures than pure C49 TiSi2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109040
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  • 9
    Electronic Resource
    Electronic Resource
    Stresses and morphological instabilities in silicide/polycrystalline Si layered structures (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2637-2639 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evolution of stress in silicide/polycrystalline Si (poly-Si) layered structures has been monitored in situ in the temperature range of 25–700 °C. At elevated temperatures, the silicide/poly-Si structure becomes morphologically unstable. The grain growth of poly-Si leads to an inversion of the positions of the two layers. The in situ stress measurement shows that this structural degradation is accompanied by a substantial increase in tensile stress of around 0.4 GPa, for NiSi, Pd2Si, and PtSi. A simple calculation indicates that the magnitude of the stress increase can be accounted for, at least to a large extend, by the volume contraction caused by the grain growth of poly-Si.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109270
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  • 10
    Electronic Resource
    Electronic Resource
    Polytype formation in zirconium-silicon thin films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 241-246 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure of zirconium silicide (ZrSi2, orthorhombic C49; a=0.369 nm, b=1.47 nm, c=0.366 nm) thin films has been investigated by high-resolution electron microscopy. The crystals are heavily faulted in the 010 plane with an average distance between faults of 1.6 nm. The fault has been found to be a π/2-rotation twin around the b axis, the habit plane lying between two silicon layers. The crystals contain an equal number of 〈a〉- and 〈c〉-oriented slabs, giving rise to a strained lattice with an average a=c lattice parameter. On the basis of an elastic calculation, the fault energy is evaluated to be of the order of 5 ergs cm−2. This low energy explains the tendency to form polytypes which are mostly disordered, although some ordered sequences are favored at short range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345295
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