Threshold Voltage Variations Induced by SiGe and SiC of Sub 5-nm Node Silicon Nanosheet Field-Effect Transistors.

In this paper, we investigated the threshold voltage () variations in sub 5-nm node silicon nanosheet FETs (NSFETs) caused by Ge and C diffusion into NS channels using fully-calibrated 3-D TCAD simulation. Ge (C) atoms of SiGe (SiC) source/drain (S/D) diffuse toward the NS channels in lateral direction in -type (-type) FETs, and Ge atoms of SiGe stacks diffuse toward the NS channels in vertical direction. Increasing Ge mole fraction of the SiGe S/D in the -type FETs (PFETs) causing increasing compressive channel stress retards boron dopants diffusing from the SiGe S/D into the NS channels, thus increasing the of PFETs (). However, the decreases as the Ge mole fraction of the SiGe S/D becomes greater than 0.5 due to the higher valence band energy () of the NS channels. On the other hand, the of -type FETs (NFETs) () consistently increases as the C mole fraction of the SiC S/D increases due to monotonously retarded phosphorus dopants diffusing from the SiC S/D into the NS channels. On the other hand, the and consistently decreases and increases, respectively, as Si/SiGe intermixing becomes severer because both and conduction band energies () of the NS channels become higher. In addition, the variations are more sensitive to the Si/SiGe intermixing than the variations because the Ge mole fraction in NS channels affects the remarkably rather than the . As a result, the Ge atoms diffusing toward the NS channels should be carefully considered more than the C diffusion toward the NS channels for fine variation optimization in sub 5-nm node NSFETs.