Surface characterization of nickel germanides for Schottky source/drain contacts to germanium p-MOSFETs

Germanium is of unique interest for CMOS technology because of its high electron and hole mobilities compared with those of its counterpart silicon [1]. Significant progress has been in germanium p-MOSFETs, while in n-MOSFETS there are some hindrances. The diffusivity and poor activation of dopants in Ge [2] will not allow the formation of shallow junctions and low resistivity source and drain regions in Ge MOSFETs. Implantless fabrication with nickel germanide Schottky source and drain contacts is an alternative approach to fabricate Ge p-MOSFETs. S. Zhu et al [3] demonstrated the fabrication of nickel germanide based p-MOSFETs. D. R. Gajula et al [4] showed the effect of RTA temperature on the Schottky barrier height (Φ_bn) of nickel germanides on Ge and observed Φ_bn of 0.6-0.7 eV for RTA at approximately 300°C. So the barrier height for holes (Φ_bp = E_g-Φ_bn) is nearly zero, which is suitable for Schottky based p-MOSFETs. Electrical characterization of NiGe/Ge diodes was used to measure the Schottky barrier height. Surface characterization of these nickel germanides is very important in optimizing the fabrication of germanide based Ge p-MOSFETs. In this work, we show the surface characterization of nickel germanides formed on germanium with different RTA treatments by using SEM, XRD and XPS techniques.