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

Abstract

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.