Nickel silicides and germanides: Phases formation, kinetics and thermal expansion

Thin film germanide reactions are often declared to be the same as silicides reactions which were far more studied. In this paper, we present a comparative study of the phase formation and kinetics of nickel silicides and nickel germanides by several experimental techniques. The samples, composed of a nanometric nickel film (50 nm) deposited on silicon or germanium substrates, have been examined by several “in situ” real time measurements: X-ray diffraction (XRD), and differential scanning calorimetry (DSC). These original DSC and “in situ” XRD measurements have allowed us to determine the interfacial reaction rate for Ni2Si using a linear-parabolic law. During the relatively fast DSC ramp, the growth is mainly controlled by the interface while isothermal heat treatments lead to a mainly diffusion control. In contrary to what is usually found for nickel silicide and germanides, a simultaneous growth of Ni5Ge3 and NiGe has been found during “in situ” XRD measurements. The different behavior between the Ni–Si system (sequential formation) and the Ni–Ge system (simultaneous formation) is interpreted in term of diffusion and interface controlled growth. In addition, in devices, the film stability and the stress of the silicides or the germanides can be affected by an important physical characteristic that is the anisotropy of dilatation coefficient. In this work, the lattice parameters and linear thermal expansion coefficients (γa, γb and γc) of the orthorhombic Ni(Si1 − XGeX) compounds with 0 ≤ X ≤ 1 were determined from high temperature X-ray diffraction data (298–1073 K). A negative thermal expansion coefficient of the b lattice parameter of Ni(Si1 − XGeX) for all the studied Ge concentration was observed: the magnitude of this negative thermal expansion coefficient is decreasing with increasing Ge concentration.