Low leakage and high performance of nMOSFET using SiGe layer as a diffusion barrier

As a boron diffusion barrier, a 20 nm-thick Si0.8Ge0.2 layer was successfully utilized in n-channel MOSFETs for implementing a retrograded well structure. Compared with the conventional Si CMOS process, the developed n-channel MOSFET process provides an enhanced transconductance (7%) and lower sub-threshold swing which is nearly unchanged even at an increased drain-source voltage. Especially, because sub-threshold leakage current is one of the key issues in the MOS device scaling due to reduced threshold voltage, the usage of a Si0.8Ge0.2 layer in n-channel MOSFET was verified to be useful for low power and high performance even under aggressive scaling constraints.