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

The Ni silicidation of polycrystalline-Si∕SiO2 gates with 25nm 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 (tNi) and polycrystalline-Si (tSi) thicknesses (e.g., tNi∕tSi∼0.55, 1.09, 1.37, and 1.64 for stoichiometric NiSi, Ni2Si, Ni31Si12, and Ni3Si, respectively). In contrast, they demonstrate that on 25nm lines, the resulting films can contain Ni31Si12 and Ni3Si even for deposited tNi∕tSi as low as 0.6. They found, however, that the phase formation sequence and required thermal budgets were similar on 25nm lines (tNi∕tSi∼0.6 and 1.2) to those on blanket films with thicker Ni (tNi∕tSi∼1.7). This suggests that the nucleation and phase formation kinetics of Ni sil...