Channel doping impact on FinFETs for 22nm and beyond

The natural choice to achieve multiple threshold voltages (V_th) in fully-depleted devices is by choosing the appropriate gate workfunction for each device. However, this comes at the cost of significantly higher process complexity. The absence of a body contact in FinFETs and insensitivity to back-gate bias leaves the conventional channel doping approach as the most practical technique to achieve multiple V_th. This choice, however, introduces a variable that is usually not considered in the context of fully depleted devices. For the first time, we demonstrate a multiple V_th solution at relevant device geometries and gate pitch for the 22nm node. We investigated the impact of FinFET channel doping on relevant device parameters such as T_inv, mobility, electrostatic control and V_th mismatch. We also show that V_th extraction by the “constant current” method could mislead the DIBL analysis of devices with greatly different channel mobility.