Sub-10-nm-Diameter InGaAs Vertical Nanowire MOSFETs: Ni Versus Mo Contacts

Recently, sub-10-nm-diameter InGaAs vertical nanowire (VNW) MOSFETs have been demonstrated. The key to this achievement was the use of Ni for the top ohmic contact. In this paper, we present a detailed study of the impact of Ni and Mo contacts on the electrical characteristics of highly scaled InGaAs VNW MOSFETs. Sequential annealing experiments are presented that reveal the optimum temperature for each type of contact. A negative temperature dependence of the ON-resistance of 7-nm-diameter Ni-contacted devices suggests the existence of an energy barrier. We also observe an unexpected transconductance and drain-induced barrier loweirng (DIBL) dependence on transistor diameter in Ni-contacted devices as well as abnormal DIBL asymmetry to swapping source and drain. All these results can be explained by Ni diffusing down the nanowire during the contact annealing process, reducing the effective channel length, and creating a Schottky-barrier drain.