Interface Stability of Ti(Si_l−yGe_y)₂ and Si_1−x Ge_x Alloys

AbstractThe stability of C54 Ti(Si1−yGey)2 films in contact with Si1−xGex substrates was investigated. The titanium germanosilicide films were formed from the Ti − Si1−xGex solid phase metallization reaction. It was observed that Ti(Si1−yGey) 2 initially forms with the same germanium content as the Si1−x Gex substrate (i.e., y = x). Following the initial formation of TiM2 (M = Sil−yGey), silicon and germanium from the substrate diffuse into the TiM2 layer, the composition of the TiM2 changes, and Si1−z Gez precipitates form along the TiM2 grain boundaries. The germanium content of the Ti(Sil−y Gey)2 decreases, and the Sil−z Gez precipitates are germanium rich such that y &lt; x &lt; z. This instability of the TiM2 film and the dynamics of the germanium segregation were examined using the Ti-Si-Ge ternary equilibrium diagram. The relevant region of the ternary diagram is the two phase domain limited by a Si-Ge solid solution and a TiSi2 − TiGe2 solid solution. In this study first approximation Ti(Sil−y Gey)2 -to- Sil−xGex tie lines were calculated on the basis of classical thermodynamics. The tie line calculations indicate that for C54 Ti(Sil−yGey)2 to be stable in contact with Sil−xGex, the compositions of the two phases in equilibrium must be such that y &lt; x. The specific compositions of the two phases in equilibrium depend on the temperature and the relative quantities of the two phases. The dynamic processes by which the Ti(Si1−yGey)2/Si1−x. Gex, system progresses from the as-formed state (y = x) to the equilibrium state (y &lt; x) can be predicted using the tie line calculations.</jats:p

Radioactive Ni* Tracer Study of the Nickel Silicide Growth Mechanism

A tracer technique using radioactive 56Ni* was applied to investigate the growth mechanisms ofNi2Si, NiSi and NiSi2 on Si&lt;100&gt; and Si &lt;111&gt; wafers. A thin Ni* tracer layer initially at the Ni-Si interface was observed to migrate and spread during the growth of nickel silicides at 350, 450 and 800°C. These data are discussed, together with other results from 31Si* tracer work and xenon marker experiments. Ni appears to be the dominant moving species in all cases, diffusing both substitutionally and by grain boundary paths (in comparable amounts) for Ni2Si and substitutionally for NiSi and NiSi2.</jats:p