Effect of composition on phase formation and morphology in Ti–Si1−xGex solid phase reactions

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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.