In‐Situ Observation of the Formation of NiSi/Ni₂Si Heterojunction in SiGe Nanowire with Al₂O₃ Diffusion Barrier Layer

Abstract

In complementary metal‐oxide‐semiconductor technology, the metal silicides/germanides have prominent advantages such as low resistivity, high thermal and chemical stability. Here, a study to probe the phase transformations and the diffusion behaviors of Ni in Si1‐xGex nanowire (NW) by in situ transmission electron microscopy is conducted. The Si1‐xGex NWs are dispersed on Si3N4 membrane and contacted with Ni by E‐beam lithography process for in situ study. The sample is heated to 723 K, Ni is diffused into Si1‐xGex NW and Ni2Si is formed accordingly. The diffusion mechanism is confirmed to be reaction‐controlled and the activation energy can be extracted to be 0.708 eV. On the other hand, in this study Al2O3 layer‐coated Si1‐xGex NW is probed for comparison, while the Al2O3 layer serves as the diffusion barrier to modulate the diffusion rate of Ni. This increases the activation energy to 1.38 eV. Importantly, it is found that the NiSi/Ni2Si heterojunction is formed at the diffusion front. The results provide the insights for fabrication of semiconducting devices.