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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
    Formation of C54 TiSi2: Effects of niobium additions on the apparent activation energy (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6409-6415 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation of C54 TiSi2 using Ti–Nb alloys deposited on polycrystalline Si substrates was studied by means of in situ x-ray diffraction and resistance measurements during temperature ramping. Alloys with Nb contents ranging from 0 to 13.6 at. % were used. The formation temperature of C54 TiSi2 was reduced in the presence of Nb. However, the addition of Nb in Ti did not cause fundamental changes in the evolution of resistance versus temperature. This latter observation suggests that the mechanism for the formation of C54 TiSi2 remained the same in spite of the enhancement effect. For alloys with up to 8 at. % of Nb, the C49 TiSi2 phase formed first, as with pure Ti. When annealing the alloy with 13.6 at. % Nb, neither C49 TiSi2 nor C54 were found in the usual temperature ranges, instead, C40 (Nb,Ti)Si2 was observed. This phase transformed to C54 (Nb,Ti)Si2 above 950 °C. The apparent activation energy associated with the formation of C54 TiSi2 was obtained by annealing the samples at four different ramp rates from 3 to 27 K/s; it decreased continuously from 3.8 to 2.5 eV with increasing Nb content from 0 to 8 at. %. The apparent activation energy for the formation of C40 (Nb,Ti)Si2 was found to be 2.6 eV. The possible physical meaning, or lack thereof, of the high activation energies derived from experimental measurements is extensively discussed. A qualitative model is proposed whereby nucleation would be rate controlling in pure TiSi2, and interface motion in samples with 8 at. % Nb. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1413952
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  • 7
    Electronic Resource
    Electronic Resource
    Comment on "Dominant diffusing species during cobalt silicide formation" [J. Appl. Phys. 79, 153 (1996)] (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 8216-8217 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The report that during the formations of the isomorphous CoSi2 and NiSi2 the dominant diffusing species are different is questioned. Not only does this contradict previous results obtained with inert gas markers, but it is based on experiments carried out with Ta markers that are not inert. The problem of using markers in determining the dominant diffusing species during thin film reactions is briefly analyzed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373526
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  • 8
    Electronic Resource
    Electronic Resource
    Kinetics of silicide formation measured by in situ ramped resistance measurements (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4087-4095 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of "Kissinger'' plots to analyze in situ resistance monitoring of thin-film reactions during heating at a constant rate is widely accepted. One obtains the activation energy for diffusion, at least in the case of diffusion-controlled reactions. The aim of this article is to extend the analysis one step further and show that, provided that the thickness of the layers formed is known, the same experimental and analytical techniques may yield the pre-exponential growth factor. The validity of the procedure is demonstrated by comparing the results thus obtained with data from the literature derived by conventional analysis of compound growth during isothermal annealing. Such comparisons have been made for Co2Si, CoSi, CoSi2, Pt2Si, PtSi, Ni2Si, and NiSi formation on undoped polycrystalline Si and single-crystal Si on sapphire substrates with ramp rates ranging from 10−2 °C/s to 102 °C/s. Measurements used both conventional furnace and rapid thermal annealing. In the past, the common practice has been to use the Kissinger method regardless of the sequence of growing phases. However, for phases other than the first one to be formed the direct Kissinger analysis needs to be modified. In the present cases the results obtained by means of an appropriately corrected procedure are not significantly different; that may not always be true. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361771
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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Enhanced thermal stability of C49 TiSi2 in the presence of aluminum (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 312-314 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The introduction of a thin layer of Al at the interface between Ti films and Si substrates enhances the formation of C49 TiSi2 and retards the transition from C49 to C54. An Al interlayer, 0.64 nm thick, reduces the time required to form C49 TiSi2 isothermally at 500 °C from 14 to 7 min. The C49–C54 transformation temperature is increased from 767 to 853 °C, when heating the samples at a constant ramp rate of 3 K/s. Most of the Al is found toward the interface between a Ti-rich silicide at the surface and TiSi2, rather than at the interface between TiSi2 and the Si substrate. The grain size of the C49 TiSi2 formed in the presence of Al is about five times smaller than that formed on a control sample with pure Ti, indicating that the increased density of grain boundaries in C49 TiSi2 in the presence of Al does not help the C49–C54 transformation. Therefore, the improved thermal stability of C49 TiSi2 is likely to be caused by other factors such as a reduced electron/atom ratio when replacing Si with Al in the disilicide. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121853
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