Effect of bilayer geometry on the diffusion of Ni in amorphous Si and the consequent growth of silicides

Abstract

The deposition and annealing of nickel-amorphous silicon (a-Si) bilayer thin films on fused silica substrates is reported. Two bilayer geometries that consisted of an a-Si layer and the Ni layer over and below it, respectively, are investigated. The bilayers were deposited at temperatures between 200 and 550 °C, and in each case, postdeposition annealed in vacuum at the temperature of deposition to study the effect of geometry on the diffusion process. The diffusion process is illustrated using cross-sectional scanning electron microscopy in conjunction with energy dispersive spectrometry. The study reveals that, independent of geometry, the top surface of Ni/Si bilayers is abundant in Ni after annealing. In the geometry when Ni is at the top, x-ray diffraction and Raman spectroscopy studies reveal that, at temperatures <400 °C, there is no reaction between the Ni and the Si. The Ni-Si reaction occurs at temperatures >400 °C to form NiSi2. However, when Ni is at the bottom of the Si layer at a temperature of 200 °C itself, a nickel rich silicide Ni31Si12 forms. This is in addition to nanocrystallization of Ni. In the case when Nickel is at the bottom, most of the energy is taken up in diffusion and crystallization of Ni. The remaining energy is then used to react with the Si, leading to the formation of Ni31Si12 and its crystallization. At temperatures >500 °C, Ni reacts with Si to form NiSi2. When Ni is at the top, since it is already at its preferred location most of the energy is used up in crystallization of Ni and reaction of Ni with Si and crystallization of NiSi2. Importantly, in both cases, the energy is insufficient to cause crystallization of Si.

Chromium oxide as a metal diffusion barrier layer: An x-ray absorption fine structure spectroscopy study

“…However, the large contribution from the a-Si layer on the top surface of the stack suppressed the weak silicide signal. 5 In the present study, and in an earlier report, 16 investigated. X-ray Absorption Fine Structure (XAFS) technique is a powerful non-destructive tool for studying the local order around a selected element, independently on the presence of crystallinity.…”

“…4,5 In literature, the diffusion of Cr into Si and the formation of CrSi 2 phase have been studied by resistivity measurement, 3,9,10 secondary ion mass spectroscopy, 11 Hall mobility, 10 Rutherford back scattering, 12 differential optical spectroscopy, 13,14 atomic force microscopy, 13,14 cross sectional scanning electron microscopy, 5 Auger spectroscopy, 3 and X-ray photoelectron spectroscopy. 15 Although these techniques are suitable in determining the metal (Cr) diffusion in Si, no crystallographic study can be carried out.…”