Paper EM-WeM9
Microstructural Evolution of Nickel Germanides in the Ni_1-xTa_x/Ge Systems during In-situ Annealing

Wednesday, October 17, 2007, 10:40 am, Room 612

It is becoming increasingly difficult to further improve the performance of Si-based complementary metal-oxide-semiconductor (CMOS) using traditional device scaling. Ge-based devices have attracted considerable attention for high-performance logic applications on account their its lower effective mass and high carrier mobility (double for electrons and four times higher for holes compared with those in Si).¹ However, the NiGe shows a poorer thermal stability than NiSi. The limited thermal stability of NiGe may deteriorate the performance improvement of Ge metal-oxide-semiconductor field-effect transistors (MOSFETs). These features of Ge substrate motivated us to investigate the mechanism of the formation and thermal stability of NiGe and the effect of alloying elements, i.e. the tantalum which is the refractory metal. In this study, the formation and morphological evolution of the germanides formed from the Ni_1-xTa_x (~30nm)/Ge (x=0 and 0.1) systems as a function of temperature was investigated by in-situ annealing in the transmission electron microscope (TEM, JEM-3011, JEOL Co. Ltd) with a specimen heating holder. The sheet resistance of the germanides formed in the Ni_0.9Ta_0.1/Ge system was lower at temperatures above 550°C than the Ni/Ge system. Through the addition of Ta atoms, Ni germanide grain growth was retarded and the surface morphology of the Ni germanide layer improved. An approximately 10nm thick Ta-rich layer formed on the top of the germanide layer. Eventually, the agglomeration of Ni germanide was retarded and the thermal stability of the Ni germanide formed from the Ni-Ta alloy became superior to that formed from the pure Ni.

¹ C. O. Chui, S. Ramanathan, B. B. Triplett, P. C. Mclntyre, and K. C. Saraswat, IEEE Electron Dev. Lett. 23, 473 (2002).