Microstructural Evolution of Ni-Stanogermanides and Sn Segregation during Interfacial Reaction between Ni Film and Ge_1−xSn_x Epilayer Grown on Si Substrate

The Ni-stanogermanides were formed via an interfacial reaction between Ni film and a Ge1−xSnx (x = 0.083) epilayer grown on a Si substrate driven by thermal treatment, and their microstructural and chemical features were investigated as a function of a rapid thermal annealing (RTA) temperature. The Ni3(Ge1−xSnx) phase was formed at the RTA temperature of 300 °C, above which Ni(Ge1−xSnx) was the only phase formed. The fairly uniform Ni(Ge1−xSnx) film was formed without unreactive Ni remaining after annealing at 400 °C. However, the Ni(Ge1−xSnx) film formed at 500 °C exhibited large surface and interface roughening, followed by the formation of Ni(Ge1−xSnx) islands eventually at 600 °C. The Sn concentration in Ni(Ge1−xSnx) gradually decreased with increasing RTA temperature, implying the enhancement of Sn out-diffusion from Ni(Ge1−xSnx) grains during the Ni-stanogermanidation process at higher temperature. The out-diffused Sn atoms were accumulated on the surface of Ni(Ge1−xSnx), which could be associated with the low melting temperature of Sn. On the other hand, the out-diffusion of Sn atoms from Ni(Ge1−xSnx) along its interface was dominant during the Ni/Ge1−xSnx interfacial reaction, which could be responsible for the segregation of metallic Sn grains that were spatially confined near the edge of Ni(Ge1−xSnx) islands.