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  • 1
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transformation of titanium silicide from the C49 to the C54 structure was studied using x-ray diffraction of samples containing arrays of narrow lines of preformed C49 TiSi2. Using a synchrotron x-ray source, diffraction patterns were collected at 1.5–2 °C intervals during sample heating at rates of 3 or 20 °C/s to temperatures of 1000–1100 °C. The results show a monotonic increase in the C54 transition temperature by as much as 180 °C with a decreasing linewidth from 1.0 to 0.1 μm. Also observed is a monotonic increase in (040) preferred orientation of the C54 phase with decreasing linewidth. The results demonstrate the power of in situ x-ray diffraction of narrow line arrays as a tool to study finite size effects in thin-film reactions. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 1262-1265 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Self-propagating explosive reactions, with a reaction front speed of about 4 m/s, have been observed in free-standing polycrystalline Al/Ni multilayer thin films. The resultant phases and microstructures are compared with those obtained by conventional thermal annealing. We show evidence which indicates that melting occurred in the explosive reactions of films with an atomic concentration ratio of 3Al:1Ni. It is also observed that the propensity of multilayer films to undergo explosive reactions is dependent on the modulation length of the film as well as on the ambient temperature. These observations are interpreted with a simple model based on the rate balance between the rates of heat generation and heat dissipation.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 852-854 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The reaction between solid layers to form a product phase has been studied using scanning calorimetry of multilayer Nb/Al and Ni/amorphous-Si thin films. The most striking feature for both materials systems is the occurrence of two maxima in the reaction rate during the formation of a single product phase, suggesting a two step growth process. A model has been developed in which the first step is taken to be the nucleation and two-dimensional growth to coalescence of the product phase, in the plane of the initial interface. The second step is taken to be the thickening of the product layer by growth perpendicular to the interface plane. The success of this simple model in describing the principal features of the experimental results on two different materials systems suggests that nucleation is an important aspect of phase formation and selection in these thin-film reactions.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In situ resistance versus temperature or time for reactions between 32 and 57.5 nm of titanium and undoped or doped polycrystalline silicon (boron, arsenic, or phosphorus, 7.9×1019–3.0×1020/cm3) has been measured and no clear correlation was found between the activation energy for the formation of the industrially important low-resistance C54-TiSi2 phase and its formation temperature. It is also demonstrated that with certain moderate doping levels typical of complementary metal-oxide-semiconductor manufacturing, boron or phosphorus-doped polycrystalline silicon can delay the formation of C54-TiSi2 more than arsenic-doped polycrystalline silicon. Finally, by using in situ resistance measurements, it is demonstrated that the "two-step'' thermal annealing process similar to a salicide process requires less thermal annealing time at high temperatures to form C54-TiSi2 than a single "one-step'' thermal anneal at the same temperature. © 1994 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 2894-2898 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Self-propagating explosive reactions can occur in multilayer thin films. Explosive silicidation in nickel/amorphous-silicon multilayer thin films has been investigated using a combination of high-speed photography, high-speed temperature measurements, plan-view transmission electron microscopy, and thin film x-ray diffraction. The multilayer films had an atomic concentration ratio of 2 Ni atoms to 1 Si atom. The silicide phase formed by explosive silicidation was Ni2 Si. This was the same phase formed by conventional thermal annealing of the multilayer thin film. The temperature of the explosive reaction front was measured to be approximately 1565 K. The reaction-front velocity was found to vary from 22 to 27 m/s and to be at most weakly dependent on the modulation period and the total film thickness. The resulting Ni2 Si grain structure formed by explosive silicidation is less defective than Ni2 Si formed by conventional thermal annealing. This was attributed to the higher reaction temperatures and the shorter reaction times of explosively formed Ni2 Si as compared to Ni2 Si formed via conventional annealing.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 1325-1333 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Isothermal and constant-heating-rate differential scanning calorimetry, cross-sectional transmission electron microscopy, thin-film x-ray diffraction, and thermodynamic and kinetic analyses have been used to investigate silicide phase selection in nickel/amorphous-silicon multilayer thin-film reactions. The atomic concentration ratio of the films was two Ni atoms to one Si atom and the layer thickness ratio was one to one. During deposition, a thin layer of amorphous nickel silicide formed between the nickel and amorphous-silicon layers. Upon heating, this amorphous nickel silicide thickened slightly, until crystalline Ni2Si formed at the nickel/amorphous-nickel-silicide interface. Further heating caused the simultaneous growth of both the amorphous nickel silicide and crystalline Ni2Si. Comparison of thermodynamic data to kinetic models for silicide formation and the analysis of calorimetry data suggests that nucleation barriers are responsible for the initial formation of the amorphous nickel silicide and limit subsequent formation of crystalline Ni2Si.
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  • 7
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate that the temperature at which the C49 TiSi2 phase transforms to the C54 TiSi2 phase can be lowered more than 100 °C by alloying Ti with small amounts of Mo, Ta, or Nb. Titanium alloy blanket films, containing from 1 to 20 at. % Mo, Ta, or Nb were deposited onto undoped polycrystalline Si substrates. The temperature at which the C49–C54 transformation occurs during annealing at constant ramp rate was determined by in situ sheet resistance and x-ray diffraction measurements. Tantalum and niobium additions reduce the transformation temperature without causing a large increase in resistivity of the resulting C54 TiSi2 phase, while Mo additions lead to a large increase in resistivity. Titanium tantalum alloys were also used to form C54 TiSi2 on isolated regions of arsenic doped Si(100) and polycrystalline Si having linewidths ranging from 0.13 to 0.56 μm. The C54 phase transformation temperature was lowered by over 100 °C for both the blanket and fine line samples. As the concentration of Mo, Ta, or Nb in the Ti alloys increase, or as the linewidth decreases, an additional diffraction peak appears in in situ x-ray diffraction which is consistent with increasing amounts of the higher resistivity C40 silicide phase. © 1997 American Institute of Physics.
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  • 8
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report that the ion implantation of a small dose of Mo into a silicon substrate before the deposition of a thin film of Ti lowers the temperature required to form the commercially important low resistivity C54–TiSi2 phase by 100–150 °C. A lesser improvement is obtained with W implantation. In addition, a sharp reduction in the dependence of C54 formation on the geometrical size of the silicided structure is observed. The enhancement in C54 formation observed with the ion implantation of Mo is not explained by ion mixing of the Ti/Si interface or implant-induced damage. Rather, it is attributed to an enhanced nucleation of C54–TiSi2 out of the precursor high resistance C49–TiSi2 phase. © 1995 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2009-2011 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The activation energies Ea for C49 and C54 TiSi2 formation were determined using in situ resistance measurements during rapid thermal annealing. Ti films were evaporated on undoped polycrystalline Si (poly-Si) and single-crystal Si on sapphire (SOS) substrates. The resistance was monitored for heating rates from 1 to 95 °C/s up to 1000 °C. The Ea's determined from Kissinger plots were 1.86±0.23 and 1.65±0.31 eV for C49 TiSi2 formation and 3.30±0.16 and 3.67±0.13 eV for C54 TiSi2 formation for Ti/poly-Si and Ti/SOS samples, respectively. These are the first reported measurements of Ea's for C49 and C54 TiSi2 formation at such high heating rates. The formation sequence remained the same for the range of heating rates examined. © 1994 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 795-797 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the use of differential scanning calorimetry to study the temperatures and kinetics of nickel silicide formation from nickel/amorphous silicon multilayer films. When the layer thickness ratio of a multilayer film is 1:1, Ni2 Si is the only phase to form. The activation energy for this reaction is 1.5 eV and the interdiffusivity pre-exponential is found to be 6 cm−2s−1. These values are in excellent agreement with values obtained using different techniques. The temperature at which Ni2 Si formation is observed a function of layer thickness, with the thinner layers reacting at lower temperatures. This layer thickness dependence can be explained by the lower reaction times for thinner layers. Upon mechanical impact, films composed of very thin layers (〈125 A(ring)) reacted explosively at room temperature to form Ni2 Si. Explosive silicidation is presumed to occur when the rate of heat generation at the many reacting interfaces exceeds the rate of heat dissipation.
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