The formation of intermetallics in Cu/In thin films
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Suchitra Sen Central Glass and Ceramic Research Institute, Jadavpur, Calcutta-700032, India (Received 19 September 1991; accepted 6 February 1992)
The kinetics of the formation of intermetallics in the Cu-In bimetallic thin film couple have been studied from room temperature to 432 K by measuring the evolution of composite and contact electrical resistance with time and temperature. The resistivity measurements have been supplemented by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Copper reacts with indium even at room temperature to form Cuin intermetallic and assuming a model of defect assisted diffusion into the grains, the activation energy averaged over five different samples is found to be 0.40 eV. The grain boundary diffusion is found to occur with an average activation energy of 0.55 eV. XRD confirms the growth of Cuin intermetallic and on annealing at higher temperature, for copper-rich films copper further reacts with Cuin to form Cu 9 ln 4 . Further evidences of solid state reactions and grain boundary diffusion through Cu grain boundaries have been obtained from SEM study. TEM indicates the growth of the grain size on annealing and confirms the presence of the Cuin phase.
I. INTRODUCTION Binary alloy formation in bimetallic thin film couples is a field of intensive study because of their important technological and industrial applications. Thin films contain a high density of low temperature short circuits for diffusion such as grain boundaries, dislocations, and vacancies etc., so impurities in thin films invariably diffuse at lower temperatures than for bulk materials. It is seen that1 group Ib (Cu, Ag, and Au) and group Illb (In) and IVb host metals (Sn,Pb), when made into a thin film diffusion couple, can readily diffuse even at room temperature with the formation of intermetallic compounds. It is important to know the nature of interfaces as they affect the properties of the individual materials. We have studied a few such interesting systems like Ag/Sn, 2 Cu/Sn, 3 Ag/In, 4 etc. In our previous study,4 the diffusion of Ag/In bimetallic films was shown to proceed at room temperature with the rapid growth of an intermetallic phase which on further annealing transformed to another new phase. Ag/In belongs to the group of so-called fast-diffusers; the bulk diffusivity of silver is very high, almost of the order of the grain boundary diffusivity. In this paper, another fast diffuser system is chosen, Cu/In, on which until now not very much work has been reported. It was previously pointed out by Simic and Marinkovic5 that Cu reacts with In even at room temperature to form Cuin. Keppner et al.,6 using the perturbed 7-7 angular correlation method, observed that the thermal behavior of Cu/In couples supports a diffusion controlled growth mechanism. J. Mater. Res., Vol. 7, No. 6, Jun 1992
The purpose of the present study is to monitor the degree of interfacial reaction in our system, using electrical resistivity measurements for two configuratio
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