AN IN SITU REAL-TIME RBS STUDY OF SEQUENCE AND TEMPERATURE OF FORMATION OF NICKEL GERMANIDES

Abstract

The sequence of phase formation and the temperatures at which these phases form in the Ni/Ge binary system have been studied in real-time at sub-eutectic temperatures using in situ realtime Rutherford Backscattering Spectrometry (RBS). Nonconventional (i.e., with marker) thin film diffusion couples produced by depositing nanometric nickel films (47-80 nm) on Ge<100>- oriented substrates were thermally annealed in the scattering chamber by linear temperature ramping to induce solid phase reactions (SPR) between nickel and germanium. Only two phases were observed during the reaction. The first phase to nucleate was identified to be Ni5Ge3 and its growth was observed at 145 oC. The last and final phase was found to be NiGe and its growth started at 170 oC. Although the growth of phases in the thin film diffusion couple regime is known to be sequential in which one phase grows before another phase starts to grow, an unusual simultaneous growth of Ni5Ge3 and NiGe in the presence of nickel has been demonstrated in this study.