Degradation of doped Si regions contacted with transition-metal silicides due to metal-dopant compound formation

The stability of doped Si with respect to a contacting silicide is investigated for TiSi₂, VSi₂, CoSi₂, ZrSi ₂, MoSi₂, TaSi₂, WSi₂, and PtSi on As- and B-doped Si by calculation of the critical portion of the ternary diagram. From the thermodynamic calculations it is shown that high B concentrations in Si will be unstable underneath an overlaying TiSi₂, TaSi₂, and ZrSi₂ film. In the case of As-doped Si, high concentrations in Si are unstable with respect to an overlaying TiSi ₂, TaSi₂, ZrSi₂, and PtSi film. The effect of metal-dopant compound formation is not expected to occur in the case of VSi ₂, MoSi₂, and CoSi₂, and probably also not for WSi₂, on B-doped Si. It is similarly not expected to occur in the case of VSi₂, CoSi₂, MoSi₂, and WSi₂ on As-doped Si. The relevance of these thermodynamic predictions for technological applications is illustrated by experimental results on the diffusion of B and As from various implanted silicide layers. From comparison of thermodynamic properties of M-P and M-As compounds, it was shown that no advantage is expected from P over As as far as metal-dopant compound formation is concerned.