Abstract:
This work focuses on the study of the formation of silicides by the solid state reaction in the Co/Ni/Si(100) and Ni/Co/Si(100) systems. The samples are obtained by a vacuum thermal evaporation of Co-Ni and Ni-Co bilayers on Si(100) substrates followed by a thermal annealing in air in the temperature range of 300 - 800 °C. The Grazing incidence X rays diffraction (GIXRD), the Rutherford backscattering spectroscopy (RBS), the atomic force microscopy (AFM), the Raman spectroscopy and the measurement of the electric resistivity by using the our-point method are the experimental techniques employed for samples characterization.
The analysis the Co/Ni/Si(100) system annealed at 300°C shows that the nickel reacts
initially with the Si substrate to form the Ni2Si silicide, and the cobalt diffuses to form
the (CoxNi1 -x)2Si phase. Then, the Ni2Si phase transforms to the NiSi monosilicide
which remains stable up to a temperature of 600°C. In addition, Co begins to react with the silicon to form the various phases of cobalt silicide. Beyond the temperature of 500°C, the ternary (CoxNi1 -x)Si2 phase appears. The formation of this ternary phase is confirmed by the shift of the peaks in the Raman spectrum. RBS technique shows that the ternary phase (CoxNi1 -x)Si2 is formed with different concentrations of Ni and Co elements with the thickness varying between 30 and 50 nm. Electrical measurements show that the obtained ternary silicide is more considered than the binary silicides because of its low resistivity and its high thermal stability.
For the Ni/Co/Si(100) system, the analysis allows to observe the formation of different silicides at different temperatures. Indeed, it is clearly confirmed the coexistence of both CoSi and Co2Si phases at 300 °C, the formation of Ni2Si rich nickel silicide at 400 °C followed by the formation of the NiSi, this latter keeps its thermal stability up to 700 °C, and finally the formation of NiSi2 at 800 ° C. The apparition of the ternary (CoxNi1 -x)Si phase takes place at 500°C.
