UCLA

The first phase selection and the phase formation sequence between metal and silicon (Si) couples are indispensably significant to microelectronics. With increasing scaling of device dimension to nano regime, established thermodynamic models in bulk and thin film fail to apply in one dimensional (1-D) nanostructures. Herein, we use a kinetic competition model to explain the phase formation sequence of 1-D nickel (Ni) silicides: multiple Ni silicides coexist at the initial stage and then the fastest one wins out as the first phase in a following growth competition. With kinetic parameters extracted from in-situ transmission electron microscope (TEM) observations, we quantitatively explain the unique size dependant first phase formation and the phase formation sequence changes in 1-D structures. We can further control the first phase by selectively enhancing or suppressing the growth rate of silicides through template structure modifications. Growth rate diffusion limited phases can be greatly enhanced in a porous Si nanowire (NW) template due to short diffusion paths. On the other hand, a thick aluminum oxide (Al₂O₃) shell around the NW is applied to impede the growth of large volume diffusion limited phases including Ni₃₁Si₁₂, theta-Ni₂Si and delta-Ni₂Si. Moreover, a thin platinum (Pt) interlayer between Si and Ni is used to suppress the nucleation of NiSi₂. Together, with the thick shell and Pt interlayer, we can suppress all competing silicides and render slow growing NiSi to form as the first phase. The resistivity of Pt doped NiSi (denoted as Ni(Pt)Si) NW are found compatible to pure NiSi from a two terminal and four terminal measurement. Controlled formation of Ni₃₁Si₁₂, theta-Ni₂Si, delta-Ni₂Si, NiSi or NiSi₂ as the first phase has also been achieved. To examine the kinetic competition model, 1-D cobalt (Co) and palladium (Pd) silicide formations are also studied and analyzed kinetically. A thick shell is found effective to suppress the Pd silicide NW broken at the interface.