Interface and nanostructure evolution of Cobalt Germanides on Ge(001)

Cobalt germanide (CoxGey) is a candidate system for low resistance contact modules in future Ge devices in Si-based micro- and nanoelectronics. In this paper we present a detailed structural, morphological, and compositional study on CoxGey formation on Ge(001) at room temperature metal deposition and subsequent annealing. Scanning tunnelling microscopy and low energy electron diffraction clearly demonstrate that room temperature deposition of approximately four monolayers of Co on Ge(001) results in the Volmer Weber growth mode, while subsequent thermal annealing leads to the formation of a Co-germanide continuous wetting layer which evolves gradually towards the growth of elongated CoxGey nanostructures. Two types of CoxGey nanostructures, namely flattop- and ridge-type, were observed and a systematic study on their evolution as a function of temperature is presented. Additional transmission electron microscopy and x-ray photoemission spectroscopy measurements allowed us to monitor the reaction between Co and Ge in the formation process of the CoxGey continuous wetting layer as well as the CoxGey nanostructures.