Characterization of ultra-thin nickel–silicide films synthesized using the solid state reaction of Ni with an underlying Si:P substrate (P: 0.7 to 4.0%)

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The solid state reaction of an ultra-thin Ni film (6nm) with Si:P epi layers (P: 0.7 to 4.0%), grown on 300-mm Si wafers, is studied as a function of different rapid thermal process (RTP) annealing temperatures (250–550°C) before and after applying a selective etch. The films are characterized using sheet resistance (Rs), mass, glancing incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR) atomic force, scanning electron and transmission electron microscopy (AFM, SEM and TEM) analyses to follow the onset of the Ni reaction, the evolution of the different phases formed within the Ni–Si system and to investigate the NiSi film properties. Results demonstrate that, though the Ni conversion to form an intermediate Ni-rich silicide phase is complete at 300°C, showing no dependency on the P content, the complete transformation (to form low resistive NiSi) shows a temperature dependence with P content (350°C vs 400°C for 0.7% P and 2.0–4.0% P). Despite the delay in silicidation completion, the NiSi films exhibit comparable layer properties, for all P contents. All films show a uniform conversion with a similar volume expansion (2.1), good interface properties, comparable resistivity (18–20μΩ·cm) and exhibit a smooth morphology with limited rms roughness increase (0.37 to 0.56nm). The thermal stability studies carried out on NiSi, post RTP anneals, shows a different Rs stability (650 and 575°C for 0.7% and 2.0–4.0% P), while the morphological and phase stability is found to be similar (≤500°C) for all P contents. The contact resistance measured using Circular Transmission Line Model (CTLM) structures for the synthesized NiSi films is found to be 4.8×10−8 and 1.2×10−8Ω·cm2 for 0.7% and 4.0% P respectively, the latter meeting the requirements for 10-nm CMOS technology node as predicted by International Technology Road Map for Semiconductors (ITRS).