Analysis of the diffusion controlled growth of cobalt silicides in bulk and thin film couples

Abstract

The solid state reaction between Co and Si has been studied in bulk diffusion couples between 850 and 1100 °C. At the scale of the observations made, the three phases Co2Si, CoSi, and CoSi2 are found to grow simultaneously, according to diffusion controlled kinetics. The results are analyzed in term of the Nernst-Einstein equation that directly relates diffusion fluxes to the free energy changes driving the formation. The growth rates obtained for CoSi2 at high temperatures, in the present bulk samples, are compared with those determined by others in thin films, at much lower temperatures. The comparison requires that attention should be paid to two factors. The first one is that the laws of growth are slightly different for a phase growing simultaneously with two other ones (bulk) and one phase growing alone (thin films). The second factor is the grain size of the various samples, which varies with the temperature of reaction. Once this is done, excellent agreement is obtained between the two sets of measurements. Moreover it is shown that knowing the grain size, it is possible to calculate quite accurately the growth rate from the respective isotope diffusion coefficients both for lattice and grain boundaries of Co and Si in CoSi2.

Grain Boundary Diffusion in Metals: Recent Developments

“…Other feature, which should be explained, is the large ratio of the activation enthalpies of GB and bulk diffusion, which can amount up to 0.9 and even higher. 51,54) Recently, experimental data on GB diffusivity of interphase boundaries in technologically important polysynthetically twinned (PST) TiAl alloy were obtained. 56) Titanium diffusion along the 2 = boundaries turned out to be similar to the Ti GB diffusivity of the Al-richest 2 -Ti 3 Al phase and by two orders of magnitude smaller than Ti GB diffusion in the -TiAl.…”

Grain boundary diffusion metals versus non-stoichiometric compounds

“…The most reliable measurements have been carried out on transition-metal aluminides: Ni3A1 [52], Fe3A1 [53]; on FeCo [53]; on transition-metal silicides: Ni2Si [54], Ni2Si5 [56] and CoSi2 [56], as well as on NiSb [57]. In all these compounds, the measurements were carried out for diffusion of the transition element.…”

“…Because A1 and Si have no isotopes convenient for radiotracer measurements, their GB diffusion has not been studied so far. In a few cases, such as Ni2Si [54] and CoSi2 [56], the isotope 68Ge was used as a substitute for Si. Except in Ni3A1 and FeCo [53], the ratio Eb/E turned out to be unusually high, certainly higher than for self-diffusion in pure metals.…”

“…Except in Ni3A1 and FeCo [53], the ratio Eb/E turned out to be unusually high, certainly higher than for self-diffusion in pure metals. For example, EriE = 0.9 for Co diffusion in CoSi2 [56] and 0.7 for Ni diffusion in Ni2Si [54] and NizSi 5 [55]. For Ni diffusion in Ni3A1 [52], Eb/E varies between 0.38 and 0.54 depending on the stoichiometry.…”

Lateral propagation of intermetallic phases in coarse- and nano-grained Cu/Sn diffusion couples

“…E. Geguzin in his numerous original papers and monographs [4][5][6]. Last years, in view of the technological importance of nanomaterials in the design and fabrication of integrated circuits, a number of fundamental studies have appeared concerning reactive interdiffusion in thin metal films [7,8] with the purpose to find difference in the growth kinetics of chemical compounds in nanograined thin films compared to coarse-grained materials. These studies were carried out using diffusion couples, in which one of the components was deposited onto another so that the depth of the diffusion zone was restricted by In the present study, we compare the phase propagation rates in nano-grained thin-film diffusion couples and in coarse-grained massive couples to separate contribution of GB interdiffusion to the kinetics and to give evidence of phase propagation along individual GBs.…”