Influence of work function variation of metal gates on fluctuation of sub-threshold drain current for fin field-effect transistors with undoped channels

Influence of work function variation (WFV) in metal gates (MGs) on fluctuation of sub-threshold drain current is investigated in detail by analyzing fluctuation of current-onset voltage (COV) for fin field-effect transistors (FinFETs) with polycrystalline TiN and amorphous TaSiN MGs. The polycrystalline TiN MG exhibits anomalously increased COV fluctuation of the nMOS FinFETs in comparison to the pMOS case, while the amorphous MG exhibits well suppressed COV fluctuation both for the n- and pMOS FinFETs. Through the discussion with regard to the WFV due to the polycrystalline TiN grains, it is concluded that the sub-dominant grains of TiN with lower work function (WF) in TiN form localized potential valleys in the channel of the nMOS FinFETs resulting in the anomalous leak current in the sub-threshold condition. In the pMOS FinFETs, in contrast, the lower WF grains in TiN form localized potential peaks for holes, which have less impact on the sub-threshold leakage.