Radiotracer study of cobalt diffusion and solubility in electronic-grade germanium wafers

The diffusion rate of Co in Ge is found to be as fast as 2×10^-6cm²s^-1 at 900 °C, whereas the Co solubility comes close to 1×10¹⁶cm^-3 at the same temperature. Based on these properties and its acceptor activity, Co may cause serious contamination problems during the fabrication of Ge-based electronic devices. In contrast to an early radiotracer study, we observe common diffusion profiles of complementary error function type, which are indicative of a constant diffusivity depending only on temperature. A preliminary analysis of the data points to the dissociative diffusion mechanism involving interstitial–substitutional exchange via vacancies. However, in contrast to Cu, which migrates via the vacancy-controlled mode of the dissociative mechanism, the diffusion of Co may be rate-limited by the transport properties of its interstitial modification (Coi).

Source: Physica B: Condensed Matter

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