Direct evidence of linewidth effect: Ni31Si12 and Ni3Si formation on 25 nm Ni fully silicided gates.

The Ni silicidation of polycrystalline-Si/SiO₂ gates with 25 nm linewidth was studied by x-ray diffraction and compared to that of blanket films. The authors found direct evidence of a linewidth effect in Ni full silicidation (FUSI), with formation of Ni-richer silicides at short gate lengths, and attribute it to the excess availability of Ni from regions surrounding the gate. On blanket films, the end silicide phase can be controlled by the deposited Ni (t_Ni) and polycrystalline-Si (t_Si) thicknesses (e.g., t_Ni/t_Si∼0.55, 1.09, 1.37, and 1.64 for stoichiometric NiSi, Ni₂Si, Ni₃₁Si₁₂, and Ni₃Si, respectively). In contrast, they demonstrate that on 25 nm lines, the resulting films can contain Ni₃₁Si₁₂ and Ni₃Si even for deposited t_Ni/t_Si as low as 0.6. They found, however, that the phase formation sequence and required thermal budgets were similar on 25 nm lines (t_Ni/t_Si∼0.6 and 1.2) to those on blanket films with thicker Ni (t_Ni/t_Si∼1.7). This suggests that the nucleation and phase formation kinetics of Ni silicides, including Ni₃₁Si₁₂ and Ni₃Si, are not significantly affected by the small dimensions. They also demonstrated NiSi FUSI phase control down to 25 nm, by controlling the reacted Ni to Si ratio through the reaction thermal budget. These results indicate that Ni FUSI is an attractive option for future nodes. [ABSTRACT FROM AUTHOR]