Structural changes and peculiarities of NiPdSi formation investigated by Raman and Auger spectroscopy

Abstract

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.

On the nucleation of PdSi and NiSi2 during the ternary Ni(Pd)/Si(100) reaction

“…The PdSi formation at temperatures significantly below the widely accepted nucleation temperature in the pure Pd-Si system does not result from the effect of entropy of mixing due to the direct formation of a Ni 1-x Pd x Si solid solution, as previously suggested. 8,[10][11][12][13][14] Rather, it is triggered by a reduction in surface energy, induced by the presence of the isomorphous NiSi phase. The coexistence of NiSi and PdSi transforms into a Ni 1-x Pd x Si solution at higher temperatures, which in turn results in an improved monosilicide stability by postponing NiSi 2 nucleation due to entropy of mixing.…”

“…8,9 The effect is generally explained similar to Pt by stating that a Ni 1-x Pd x Si solid solution forms. 8,[10][11][12][13][14] On the other hand, significant differences between the Pt-Si and Pd-Si solid phase reaction imply that the formation of a Ni 1-x Pd x Si solid solution cannot be simply assumed. Although the binary reaction sequences for both elements are similar, i.e., M !…”