Formation of NiGe through germanium oxide on Ge(001) substrate

Germanium based devices are of interest due to their performance potential. The use of germanium as source and drain requires low resistance access achieved by the formation of germanide (metal-germanium compound). The nickel mono-germanide (NiGe) is claimed to be the best candidate since it presents suitable electrical and thermo-kinetic qualities. However, since the germanium oxidizes instantaneously in air, we provide in this paper a study of reactions between a nanometric Ni film and a germanium (001) substrate in the presence of a native or controlled grown germanium oxide. The goal is to study the influence of the germanium oxide onto germanidation process. We report that whatever the germanium oxide types (native or grown) formation of nickel germanides can occur unlike to silica which inhibits metal/silicon reactions. Numerous characterizations such as XRD, TEM, EFTEM, SIMS and SEM lead us to propose a model. Whatever the oxide type as thick as 8 nm, nickel reacts with GeO2 during its deposition and transforms into a continuous germanate layer allowing NiGe nucleation on Ge substrate. After heat treatment the entire pure Ni film has reacted while the germanate NixOyGez were present. This means that Ni transport occurred even through germanate. Finally, this NixOyGez film shifted toward the surface as a discontinued layer. (C) 2013 Elsevier B.V. All rights reserved.