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.