Stability of As and B doped Si with respect to overlaying CoSi₂ and TiSi₂ thin films

The thermodynamic equilibrium of structures consisting of a thin film silicide (TiSi₂ or CoSi₂) on doped Si (with As or B) is investigated. Isothermal sections of the ternary phase diagrams for Ti–Si–B, Co–Si–B, Ti–Si–As, and Co–Si–As have been evaluated, indicating the stability of high B concentrations in Si underneath a CoSi₂ layer, the instability of high As concentrations in Si underneath a CoSi₂ layer, and of B and As concentrations underneath a TiSi₂ layer. The obtained thermodynamic predictions agree very well with experimental results (i) on the redistribution of dopants during silicide formation, (ii) on the diffusion of dopants from an ion implanted silicide, and (iii) on the stability of highly doped regions underneath the silicide, both for the case of TiSi₂ and CoSi₂. It is shown that even though the inaccuracy of reported thermodynamic data is substantial, thermodynamic calculations provide a useful guidance and are consistent with the experimental results.