Metal Grain Granularity Study on a Gate-All-Around Nanowire FET

Abstract

The impact of the metal grain granularity (MGG) variations on subthreshold and ON-current of a 22-nm gate length Si gate-all-around (GAA) nanowire (NW) field-effect transistor (FET) is analyzed by assessing five figures-of-merit: threshold voltage ( ${V}_{T}$ ), OFF-current ( ${I}_{ \mathrm{\scriptscriptstyle OFF}}$ ), subthreshold slope (SS) and drain-induced-barrier-lowering at low ( ${V}_{D}={50}$ mV) and high ( ${V}_{D}={1.0}$ V) drain biases, and ON-current variability at the high drain bias. We assume a TiN metal gate with four grain sizes (GS): 10, 7, 5, and 3 nm. The simulations carried out employ: 1) a 3-D finite element (FE) drift-diffusion (DD) simulator with density-gradient (DG) quantum corrections (QC) in the subthreshold region and 2) a 3-D FE Monte Carlo (MC) simulation toolbox with Schrodinger equation QC for the ON-current. We have found that the ${\sigma }{V}_{T}$ due to the MGG variability is 10% higher in the GAA-NW FET (GS of 10 nm) than in a 20-nm gate FinFET. For a GS of 3 nm, the variability becomes comparable between the GAA-NW FET and the FinFET. Comparison against the line-edge-roughness (LER) variability shows that the MGG (GS of 10 nm) affects ${\sigma }{V}_{T}~92$ % more than the LER (root-mean-square height of 0.85nm and correlation length of 20 nm). Finally, the ON-current of the FinFET (GS of 10 nm, ${V}_{D}=\textsf {0.9}$ V) has a 43% higher ${\sigma }{I}_{ \mathrm{\scriptscriptstyle ON}}$ than that of the GAA-NW (GS of 10 nm, ${V}_{D}=\textsf {1.0}$ V) making the GAA-NW FETs a much better solution for sub-10-nm technology nodes.