Work function of Ni3Si2 on HfSixOy and SiO2 and its implication for Ni fully silicided gate applications.

The effective work function (WF) of Ni₃Si₂ was evaluated on HfSi_xO_y and SiO₂ dielectrics. Ni₃Si₂ forms, in thin film Ni–Si diffusion couples with Ni to Si composition ratios between 1 and 2, after formation of a Ni₂Si/NiSi stack and by its reaction at moderate thermal budgets (comparable to those used in back end processing of complementary metal-oxide-semiconductor circuits). Ni₃Si₂ formation limits, on the Ni-rich side, the process window for NiSi fully silicided (FUSI) gates (NiSi at interface with dielectric) to reacted Ni–Si ratios <1.5. The WF of Ni₃Si₂ was found to have similar values and behavior to that of NiSi, both on SiO₂ (showing similar modulation with dopants) and on HfSi_xO_y, in contrast to Ni-richer silicides such as Ni₂Si and Ni₃₁Si₁₂ which do not exhibit significant WF modulation with dopants on SiO₂ and have considerably higher WF on HfSi_xO_y. This suggests that the chemistry and structure of the original NiSi/dielectric interface are not modified significantly by the subsequent growth of Ni₃Si₂ and implies that its formation may be tolerable when targeting NiSi FUSI gates, thereby expanding the process window for this application. [ABSTRACT FROM AUTHOR]