Ultrathin silicide films were formed by starting from 1–8 nm thick Co1−xNix (x = 0, 0.25, 0.5, 0.75, and 1) at 350 °C–900 °C. For each composition x, there exists a critical thickness above which the transition temperature from monosilicides CoSi and NiSi to a disilicide-like phase increases with increasing film thickness. Below this thickness, the disilicide phase seems to form without exhibiting the monosilicides within the detection resolution limits of transmission electron microscopy and Raman spectroscopy. Raman spectroscopic analysis seems to indicate that Ni could be dissolved in the CoSi lattice to a certain fraction despite the fact that CoSi and NiSi are distinct with different crystallographic structures. Moreover, the disorder-induced Raman scattering in NiSi2 is found to be enhanced by Co incorporation. The observed annealing behaviors are attributed to variations in free energy change for phase transition caused by differences in metal thickness.

We have demonstrated the effective Raman spectroscopy for the phase transition and phonon dynamics of NiPdSi films annealed at various temperatures. In addition to the appearance of alloy disorder-induced Raman peaks, we have shown that the presence of Pd in NiSi results not only in the retardation of NiSi2 phase transition to about 900 °C, but also in the redshift (∼3–4 cm−1) of the first-order Raman peaks. The observed Raman frequency downshift with increasing temperature can be described well by a model which has taken into account the contributions of the anharmonic, thermal expansion, and strain effects, revealing the dominant role of the phonon decay. Effects of Pd addition and annealing temperature on the Raman frequency and linewidth have been discussed. The introduction of Pd is found to reduce the Raman frequency downshift, demonstrating the favorable use of NiPdSi for microelectronics applications.

In this contribution we report on peculiarities of formation, structural and vibrational properties of compositional (alloying) nickel silicides such as NiPdSi. MicroRaman analysis has shown that NiPdSi films are thermally stable up to 900 °C, which is by 100 °C higher than that for pure NiSi films. Using Miedema's model we have calculated the heat of formation for NiPdSi to be by 4 kJ mol−1 smaller than that for pure NiSi. This demonstrates an essential role of Pd in the enhancement of thermal stability of NiSi and in retardation of NiSi2 phase formation. Raman spectra registered for NiPdSi show the peaks at wavenumbers typical for NiSi, although red shifted, as well as new Raman peaks at 322 and 434 cm−1 reported recently in [Karabko et al. J. Appl. Phys. 105, 033518 (2009)]. We have assigned these two peaks to the compositional disorder, introduced by the presence of Pd alloy. By means of Auger electron spectroscopy (AES) we have determined the peculiarities of the element distribution and Pd diffusion in NiPdSi and NiSi films, which results in a slight lack of silicon in the stoichiometry of phases and exponential decay law of Pd distribution with temperature.

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