Effect of Metal Nitride on Contact Resistivity of Metal-Interlayer-Ge Source/Drain in Sub-10-nm n-Type Ge FinFET

A metal nitride-interlayer-semiconductor source/ drain (MN-I-S S/D) model is newly proposed to investigate the effect of tantalum nitride (TaN) on the specific contact resistivity (ρc) of an MN-I-S S/D with an undoped interlayer (undoped-IL) or a heavily doped IL (n⁺-IL) in sub-10-nm n-type Ge FinFETs. In this model, the workfunction variation of TaN was considered following the Rayleigh distribution. Compared with MN-I-S structures with an undoped-IL, structures with an n⁺-IL generate much lower ρc values (i.e., ~2 × 10^-9 ω · cm²) and are less prone to variation. In addition, the impact of ρc variation on device performance is investigated using 3-D technology computer aided design simulation for undoped or heavily doped ILs in MN-I-S S/D structures. MN-I-S S/Ds with an n⁺-IL can achieve much lower current variation and a higher ON-state drive current.