From contact to diffusion controlled growth of nickel silicides in silicon nanowires

Semiconducting nanowires (NW) are implemented as the active channel of field effect transistor (FET) with linear and Schottky barrier source and drain contacts. Thermally activated axial intrusion of nickel silicides into the silicon NW from pre-patterned Ni reservoirs is used in the formation of nickel silicide/silicon contacts in SiNW FETs. In the present work, the kinetics of nickel silicide axial growth in SiNWs was analyzed in the framework of the model taking into account the balance between transition of Ni atoms from the Ni reservoir to the NW surface, diffusion transport of these Ni atoms from the contact area to the interfaces between different silicides and nickel silicide/Si interface, and corresponding reactions of Ni atoms with Si and the nickel silicides formed. Simultaneous growth of mono- and nickel rich silicide was described for different kinetic and geometrical parameters of the system. Critical parameters for transition from the linear to the parabolic dependences were introduced. The model was applied to the experimental results on nickel silicide growth in SiNWs of 25÷50 nm in diameters in a temperature range of 300÷440C°. The silicide intrusions were obtained by annealing of SiNWs with pre-patterned Ni electrodes in a rapid thermal annealing machine under nitrogen atmosphere for different temperatures and times up to 120 s. In most cases the intrusions consisted of two nickel silicides, Ni-rich and mono-silicide NiSi, as was confirmed by TEM and measuring the electrical resistance of the SiNW after full silicidation. The total intrusion length, L, and particular silicide lengths, showed various time dependences, from a linear (with low growth rates (1÷4nm/s)) to a square root, diffusion-type dependence (with higher rates (10÷15 nm/s)). This behavior is well described by the model developed.