Electrical characteristics of thin Ni2Si, NiSi, and NiSi2 layers grown on silicon
We have determined the resistivity, carrier concentration, and Hall mobility as a function of thickness (700–3000 Å) of Ni2Si, NiSi, and NiSi2 layers formed by vacuum annealing at 270÷v300°C, ≈ 400°C, and ≈ 800°C, respectively, of nickel films vacuum-deposited on a silicon substrate (111 n-type and 100 p-type Si ρ ≈ 1KΩ). The layer thicknesses were measured by 2 MeV4He+ backscattering spectrometry. The silicide phase was confirmed by x-ray measurements. The electrical measurements were carried out using van der Pauw configuration. We found the electrical transport parameters to be independent of the film thickness within the experimental uncertainty. The Hall factors were assumed to be unity. The majority carriers are electrons in NiSi and holes in Ni2Si and NiSi2. The resistivity values are 24±2, 14±1, and 34±2 μΩcm, the electron concentrations are 9±3, 10 and 7±1, and ≈ 2 × 1022 cm−3, and the Hall mobilities are 3±1, ≈ 4.5 and 6, and ≈ 9 cm2/Vs for Ni2Si, NiSi (〈100〉 and 〈111〉), and NiSi2, respectively. The systematic error in the measured values caused by currents in the high resistivity substrate is estimated to be less than 6% for the Hall coefficient. The results show that Ni2Si, NiSi, and NiSi2 layers formed by a thin film reaction are electrically metallic conductors, a result which concurs with those reported previously (1) for refractory metal silicides. The Hall mobility increases with the Si content in the silicide. The electron concentration is lowest for NiSi2 leading to the highest resistivity for the epitaxial phase of NiSi2.