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ABSTRACT: The effects of alloy composition on the electrical and structural properties of zirconium germanosilicide (Zr–Si–Ge) films formed during the Zr/Si1−xGex solid state reaction were investigated. Thin films of Zr(Si1−yGey) and C49 Zr(Si1−yGey)2 were formed from the solid phase reaction of Zr and Si1−xGex bilayer structures. The thicknesses of the Zr and Si1−xGex layers were 100 and 500 Å, respectively. It was observed that Zr reacts uniformly with the Si1−xGex alloy and that C49 Zr(Si1−yGey)2 with y = x is the final phase of the Zr/Si1−xGex solid phase reaction for all compositions examined. The sheet resistance of the Zr(Si1−yGey)2 thin films was higher than the sheet resistance of similarly prepared ZrSi2 films. The stability of Zr(Si1−yGey)2 in contact with Si1−xGex was investigated and compared to the stability of Ti(Si1−yGey)2 in contact with Si1−xGex. The Ti(Si1−yGey)2/Si1−xGex structure is unstable when annealed for 10 min at 700 °C, with Ge segregating from Ti(Si1−yGey)2 and forming Ge-rich Si1−zGez precipitates at grain boundaries. In contrast, no Ge segregation was detected in the Zr(Si1−yGey)2/Si1−xGex structures. We attribute the stability of the Zr-based structure to a smaller thermodynamic driving force for germanium segregation and stronger atomic bonding in C49 Zr(Si1−yGey)2. Classical thermodynamics were used to calculate Zr(Si1−yGey)2–Si1−xGex tie lines in the Zr–Si–Ge ternary phase diagram. The calculations were compared with previously calculated Ti(Si1−yGey)2–Si1−xGex tie lines. © 1997 American Institute of Physics.
Journal of Applied Physics 08/1997; 82(5):2342-2348. · 2.17 Impact Factor
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ABSTRACT: The effects of film thickness on the Ti–Si 1-x Ge x solid phase reaction were investigated. Thin C49 TiM 2 (M=Si 1-y Ge y ) films were formed from the solid phase reaction of 400 Å Ti or 100 Å Ti with Si 1-x Ge x alloys. It was determined that for films formed from 400 Å Ti, the nucleation barrier of the C49‐to‐C54 transformation decreases with increasing germanium content, for alloy compositions with up to ≊40 at. % germanium (i.e., x≤0.40). It was also observed that germanium segregates out of the TiM 2 lattice, for both the C49 and C54 phases, and is replaced on the TiM 2 lattice with Si from the substrate. The germanium segregation changes the Ge index y of the Ti(Si 1-y Ge y ) 2 . For films formed from a 100 Å Ti layer it was observed that the C54 TiSi 2 nucleation temperature was increased by ≥125 °C. The addition of germanium to the silicon increased the agglomeration of the C49 phase and caused the C54 TiM 2 nucleation barrier to increase further. The results also indicate that the increased temperature required for the transition to the C54 phase, for the 100 Å films, leads to an increased rate of germanium segregation. © 1995 American Institute of Physics.
Journal of Applied Physics 11/1995; · 2.17 Impact Factor
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ABSTRACT: The effects of Si1−xGex alloy composition on the Ti-Si1−xGex solid phase reaction have been examined. Specifically, effects on the titanium gcrmanosilicide phase formation sequence. C54 Ti(Si1−yGey)2 nucleation temperature, and C54 Ti(Si1−yGey)2 morphology were examined. It was determined that the Ti-Si1−xGex reaction follows a “Ti-Si-like” reaction path for Si-rich Si1−xGex alloys and follows a “Ti-Ge-like” reaction path for Ge-rich Si1−xGex alloys. The coexistence of multiple titanium germanosilicide phases was observed during Ti-Si1−xGex reactions for Si1−xGex alloys in an intermediate composition range. The morphology and stability of the resulting C54 germanosilicides were directly correlated to the Ti-Si1−xGex reaction path. Smooth continuous C54 titanium germanosilicide was formed for samples with Si1−xGex compositions in the “Ti-Si-like” regime. Discontinuous islanded C54 germanosilicides were formed for samples with Si1−xGex compositions in the mixed phase and “Ti-Ge-like” regimes. Using rapid thermal annealing techniques, it was found that the C54 titanium germanosilicides were stable to higher temperatures. This indicated that the morphological degradation occurs after C54 phase formation. The C54 Ti(Si1−xGex)2 formation temperature was examined as a function of alloy composition and was found to decrease by ≍ 70 °C as the composition approached x ≍ 0.5. An optimum Si1−xGex alloy composition range of 0 ⋚ x ⋚ 0.36 was determined for the formation of stable-continuous-low-resistivity-C54 titanium germanosilicide films from the solid phase reaction of Ti and Si1−xGex alloy. The results were described in terms of the relevant nucleation processes.
Journal of Materials Research. 10/1995; 10(11):2849 - 2863.
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ABSTRACT: The stability of C54 Ti(Si 1-y Ge y ) 2 films in contact with Si 1-x Ge x substrates was investigated. The C54 Ti(Si 1-y Ge y ) 2 films were formed from the Ti‐Si 1-x Ge x solid phase metallization reaction. It was determined that initially C54 Ti(Si 1-y Ge y ) 2 forms with a Ge index y approximately the same as the Ge index x of the Si 1-x Ge x substrate (i.e., y≊x). After the formation of the C54 titanium germanosilicide, Si and Ge from the Si 1-x Ge x substrate continue to diffuse into the C54 layer, presumably via lattice and grain boundary diffusion. Some of the Si diffusing into the C54 lattice replaces Ge on the C54 lattice and the Ge index of the C54 Ti(Si 1-y Ge y ) 2 decreases (i.e., y≪x). We propose that this process is driven by a reduction in C54 crystal energy which accompanies the replacement of Ge with Si on the C54 lattice. The excess Ge diffuses to the C54 grain boundaries where it combines with Si 1-x Ge x from the substrate and precipitates as Si 1-z Ge z which is Ge‐rich relative to the substrate (z≳x). This segregation and precipitation enhances the agglomeration of the C54 titanium germanosilicide film (i.e., lower agglomeration temperature). It was observed that rapid thermal annealing techniques could be used to reduce the annealing duration and resulted in a reduction of the Ge segregation. © 1995 American Institute of Physics.
Journal of Applied Physics 06/1995; · 2.17 Impact Factor
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ABSTRACT: We have measured and quantified the effect of alloy composition on the atomic bonding in relaxed molecular-beam-epitaxy-deposited crystalline Si1-xGex alloys. X-ray-absorption fine structure (XAFS) and x-ray diffraction were used to examine how the atomic bonding in Si1-xGex is affected by changes in alloy composition. In this study, the Ge-Ge and Ge-Si bond lengths were measured using XAFS and compared with the conflicting results of existing analytical models and previous XAFS studies. The measured Ge-Ge and Ge-Si bond lengths were found to be in good agreement with the analytical models, which predict that the Ge-Ge, Ge-Si, and Si-Si bonds maintain distinctly different lengths which change linearly with alloy composition. The topological rigidity parameter a** was used to quantify the linear dependence of the bond lengths on alloy composition and a value of a**=0.63 was calculated from the measured bond lengths. An extensive XAFS error analysis was performed and the error in the topological rigidity parameter a**=0.63-0.13+0.08 was determined. This value of a**, which is notably different from 0 or 1, indicates that both the bond lengths and bond angles are distorted by changes in composition.
Phys. Rev. B. 11/1994; 50(20).
