Interface stability of Ti(SiGe)2 and SiGe alloys: Tie lines in the ternary equilibrium diagram.

Abstract

The C54 phases of ${\mathrm{TiSi}}_{2}$ and ${\mathrm{TiGe}}_{2}$ are known to be completely miscible, however, we have observed that thin films of C54 Ti(${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Ge}}_{\mathit{y}}$${)}_{2}$ are not stable in contact with ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ when y=x. In this study it is shown that this interface instability can be related to the composition-dependent energetics that determine the Ti-Si-Ge ternary equilibrium diagram. Tie lines of the Ti(${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Ge}}_{\mathit{y}}$${)}_{2}$ to ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ system were calculated on the basis of classical thermodynamics. The calculations indicate that for C54 Ti(${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Ge}}_{\mathit{y}}$${)}_{2}$ to be stable in contact with ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$the compositions of the two phases must be such that yx. The specific compositions of the two phases in equilibrium depend on the temperature and the relative quantities of the two phases. The dynamics of the interface reactions of C54 Ti(${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Ge}}_{\mathit{y}}$${)}_{2}$ on ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ are related to the calculated tie lines, and the diffusion kinetics of the materials. Experimental results are presented that quantitatively support the model calculations. \textcopyright{} 1996 The American Physical Society.