Evolution of nickel silicide intrusions in silicon nanowires during thermal cycling

Abstract

Thermally activated axial intrusion of nickel silicides into a silicon nanowire (NW) from pre-patterned Ni reservoirs is used in formation of nickel silicide/silicon contacts in SiNW field effect transistors. This intrusion consists usually of different nickel silicides which grow simultaneously during thermal annealing. Repeated annealing is often accompanied by local thickening and tapering of the NW, up to full disintegration of the silicide segment adjacent to Si. In the present work this process was investigated for SiNWs of various diameters in between 30 and 60 nm with pre-patterned Ni electrodes after a series of rapid thermal cycles including heating, holding at different temperatures of 400-440 °C for 5-15 s and cooling to room temperature. Kinetics of the nickel silicides axial growth was analyzed in the framework of diffusion model. This model is taking into account simultaneous formation of different nickel silicide phases and balance between transition of Ni atoms from the Ni reservoir to the NW surface, diffusion transport of these Ni atoms to the interfaces between different silicides and silicide/Si interface, and corresponding reactions of the nickel silicides' formation. Additional flux of atoms caused by the NW curvature gradients due to different radii of different silicide phases was taken into account. For a certain set of parameters thickening of the nickel-rich silicide intrusion and tapering of the monosilicide part of intrusion were obtained.