Abstract
The kinetics of intermetallic compound (IMC) formation in thermally evaporated Ag-In bilayers, with In on top of Ag, was investigated using X-ray diffractometry, applied to the surfaces of the bilayer specimens, as well as scanning electron microscopy, applied to cross-sections of the bilayer specimens, prepared by a focused ion beam instrument. IMC formation was followed at room temperature as well as at elevated temperatures of 50 °C, 60 °C, and 70 °C. Two distinct growth regimes were observed coinciding with the availability of pure In. The AgIn2 IMC nucleated initially, followed by nucleation of the Ag2In IMC. The growth of AgIn2 was found to be controlled by both diffusional processes as well as interfacial reactions. The growth of the Ag2In IMC is dominantly diffusion-controlled. An interdiffusion coefficient of D=1.1±3.9·10−4 cm2 s−1 exp(−60.5±9.2 kJ mol−1R−1T−1) was obtained for the Ag2In IMC. The observations were discussed in terms of the interplay of thermodynamic and kinetic constraints.
Highlights
The kinetics of intermetallic compound (IMC) formation are commonly studied at elevated temperatures in order that sufficiently large diffusion coefficients occur
The rate controlling mechanisms are not properly discussed24 and it is left unclear which type of diffusion coefficient was determined.24. Against this background the present study provides a systematic analysis of the kinetics of IMC formation in
The temperature-resolved reactive interdiffusion measurements were limited to a maximum temperature of 70 C, as X-ray diffraction (XRD) patterns recorded at higher temperatures (i.e. 90 C) showed that the In layer had already reacted completely during the heating up of the specimen
Summary
The kinetics of intermetallic compound (IMC) formation are commonly studied at elevated temperatures in order that sufficiently large diffusion coefficients occur. Investigation of IMC formation especially at low or ambient temperatures is of great importance with a view to technical applications. During manufacturing or usage of technical devices two metals experience intimate contact and interdiffusion, and IMC formation occurring already at low temperatures between the two constituents could negatively alter the properties of the devices (see below for Ag–In alloys).. The large amount of grain boundaries in polycrystalline thin film couples, compared to bulk materials, further enhances interdiffusion and IMC formation, as these grain boundaries enhance the transport of especially substitutionally-diffusing metals as holds for In, Sn, and Pb in the Ag–In, Ag–Sn, and Ag–Pb systems
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