| 1. |
- Jarmar, T., et al.
(author)
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Germanium-induced texture and preferential orientation of NiSi1-xGex layers on Si1-xGex
- 2004
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:23, s. 1-11
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Journal article (peer-reviewed)abstract
- NiSi1-xGex films on compressively strained as well as relaxed undoped Si1-xGex epitaxially grown substrates with x=0.06-0.30 on Si(001) wafers have been studied with respect to the relative orientation of film and substrate after annealing at temperatures in the range 400-850 degreesC. Using x-ray diffraction, transmission electron microscopy, and pole-figure measurements, it was found that only the monogermanosilicide phase formed above 450 degreesC and was the only phase still at 850 degreesC. New information regarding the effects of Ge on the silicidation of Ni was also found. Thus, the preferred plane parallel to the surface is (013). Compared to NiSi, Ge suppresses the development of the other planes parallel to the surface except (013). Within this plane, the orientations of the grains pile up in such a way that the configuration NiSi1-xGex[100]//Si1-xGex[100] is avoided, which in the pole-figures leads to broad peaks in-between the substrate [100] and [010]. In addition, peaks indicating the epitaxial alignment NiSi0.8Ge0.2(+/-21-1) or (+/-2-11)//Si0.8Ge0.2(+/-2+/-20) coupled with NiSi0.8Ge0.2(+/-100)approximate to//Si0.8Ge0.2(+/-100) or (0+/-10) were found. Fine structure in the broad peaks is found to be due to lateral epitaxial alignments between grains along their common grain boundary. Based on the nonexistence of NiGe2, the observations are interpreted in terms of Ge preventing the formation of certain Ni-Ge bonds at the interface between NiSi1-xGex and the Si1-xGex substrate.
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| 2. |
- Seger, Johan, et al.
(author)
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Influence of a Si layer intercalated between Si0.75Ge0.25 and Ni on the behavior of the resulting NiSi1-uGeu film
- 2004
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 96:12, s. 7179-7182
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Journal article (peer-reviewed)abstract
- The interaction of Ni films with epitaxially grown Si-capped and not capped Si0.75Ge0.25 layers on Si(100) at 500degreesC leads to the formation of NiSi1-uGeu films as a bilayer NiSi on NiSi0.75Ge0.25 with a rather clear compositional boundary. In the absence of a Si cap at the surface, NiSi0.75Ge0.25 is formed on NiSi. Epitaxy of NiSi on NiSi0.75Ge0.25, and vice versa, occurs across the compositional boundary. The crystallographic orientation of the NiSi1-uGeu films is strongly affected by the initial layer thicknesses and the layer sequence. Without a Si cap, the NiSi1-uGeu films show an increased fiber texture with increasing Si0.75Ge0.25 thickness. In the presence of a Si cap, on the other hand, the texture collapses into a random orientation already for thin caps. Rapid diffusion of Ge at 500degreesC results in the presence of some Ge at the NiSi/Si interface for a NiSi0.75Ge0.25/NiSi/Si structure. This diffusion is accompanied by an increased roughness at the NiSi/Si interface, as compared to the quite flat NiSi/Si interface in the absence of Ge. For thin Si caps, severe interface roughening with thick NiSi0.75Ge0.25 grains protruding deeply into the remaining Si0.75Ge0.25 is observed.
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| 3. |
- Seger, Johan, et al.
(author)
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Morphological instability of NiSi1-uGeu on single-crystal and polycrystalline Si1-xGex
- 2004
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 96:4, s. 1919-1928
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Journal article (peer-reviewed)abstract
- The morphological stability of NiSi1-uGeu ternary alloy films formed by reacting Ni with single-crystal (sc) and polycrystalline (poly) Si1-xGeu is studied (u can be different from x). The agglomeration of NiSi1-uGeu films on Si0.7Ge0.3 occurs at 550degreesC after rapid thermal processing for 30 s, independently of the crystallinity of the Si1-xGeu. This behavior distinctly different from NiSi: NiSi films on poly-Si display a poorer morphological stability and degrade at lower temperatures than NiSi on sc-Si. On strained Si1-xGex, the presence of Ge simultaneously gives rise to two effects of different origin: mechanical and thermodynamic. The main driving forces behind the agglomeration of NiSi1-uGeu on sc-Si1-xGex are found to be the stored strain energy in the Si1-xGex and the larger (absolute) free energy of formation of NiSi compared to NiGe. The latter constitutes the principal driving force behind the agglomeration of NiSi1-uGeu on poly-Si1-xGex and is not affected by the degree of crystallinity of Si1-xGex. The total free-energy change also includes terms corresponding to the entropy of mixing of Si and Ge in both Si1-xGex and NiSi1-uGeu. Calculations show that the strain energy and the total free-energy change can be 5-7 times (with 30 at.% Ge) the surface/interface and grain-boundary energies in a NiSi film or the grain-boundary energy in an underlying poly-Si. These latter energies are responsible for the agglomeration of NiSi on sc- and poly-Si. The agglomeration takes place primarily via the interdiffusion of Si and Ge between Si1-xGex and NiSi1-uGeu. A structure likely to improve the stability of NiSi1-uGeu/Si1-xGex is discussed.
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| 4. |
- Zhang, Zhibin, et al.
(author)
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Different routes to the formation of C54TiSi(2) in the presence of surface and interface molybdenum : A transmission electron microscopy study
- 2002
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In: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 17:4, s. 784-789
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Journal article (peer-reviewed)abstract
- Direct evidence revealing fundamental differences in sequence of phase formation during the growth of TiSi2 in the presence of an ultrathin surface or interface Mo layer is presented. Results of cross-sectional transmission electron microscopy showed that when the Mo layer was present at the interface between Ti films and Si substrates, C40 (Mo,Ti)Si-2 formed at the interface, and Ti5Si3 grew on top after annealing at 550 degreesC. Additionally, both C54 and C40 TiSi2 were found in the close vicinity of the C40 (Mo,Ti)Si-2 grains. No C49 grains were detected. Raising the annealing temperature to 600 degreesC led to the formation of C54 TiSi2 at the expense of Ti5Si3, and the interfacial C40 (Mo,Ti)Si-2 also began to transform into C54 (Mo,Ti)Si-2 at 600 degreesC. When the Mo was deposited on top of Ti, the silicide film was almost solely composed of C49 TiSi2 at 600 degreesC. However, a small amount of (Mo,Ti)(5)Si-3 was still present in the vicinity of the sample surface. Upon annealing at 650 degreesC, only the C54 phase was found throughout the entire TiSi2 layer with a surface (Mo,Ti)Si, on top of TiSi2 Hence, it was unambiguously shown that in the presence of surface versus interface Mo, different routes were taken to the formation of C54 TiSi2.
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| 5. |
- Zhang, Zhibin, et al.
(author)
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Formation of C54TiSi(2) on Si(100) using Ti/Mo and Mo/Ti bilayers
- 2002
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In: International Journal of Modern Physics B. - 0217-9792. ; 16:1-2, s. 205-212
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Journal article (peer-reviewed)abstract
- The effect of Mo on the formation of C54 TiSi2 on Si (100) substrates is studied using crosssectional transmission electron microscopy. For a Ti/Mo bilayer on Si, the interfacial Mo film reacts with Ti and Si to form C40 (Mo,Ti)Si-2 at 550 degreesC. Crystal grains of metastable C40 TiSi2 and equilibrium C54 TiSi2 are found in the region near the interfacial (Mo,Ti)Si-2 layer due to the template phenomenon. Increasing the temperature to 600 degreesC leads to the growth of C54 TiSi2 throughout the film. No C49 grains can be detected. The findings confirm that the usual sequence for the formation of C54 TiSi2, i.e. the C49 TiSi2 forms first followed by a phase transition to the C54 TiSi2, is altered by the interposed Mo layer. For a Mo/Ti bilayer on Si, the surface Mo layer is found to be present sequentially in (Mo,Ti)(5)Si-3 at 550 degreesC, C49 (Mo,Ti)Si-2 at 600 degreesC and C54 (Mo,Ti)Si-2 at 650 degreesC. The bulk Ti beneath forms the C54 TiSi2 following the usual route through the C49-C54 phase transition. However, this transition is now enhanced, in comparison with the C54 TiSi2 formation with pure Ti, by the C54 (Mo,Ti)Si-2 atop that plays the role as a template precisely as the interfacial C40 (Mo,Ti)Si-2.
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