Impact of Random Dipole Fluctuation-Induced Variation on Nanosheet Devices

This letter reports a study on statistical variability of random dipole fluctuation-induced variation (DFV) in gate-all-around (GAA) nanosheet devices that adopt the interface dipole engineering technique for
${V} _{\text {t}}$
modulation, a new intrinsic device variability source that has yet been reported. The impact of DFV with the incorporation of La and Al is characterized by threshold voltage standard deviations (
$\sigma _{V_{\text {t}}}$
), which are 3.7–8.2-mV and 7.7–17.2-mV for the dipole-induced potential shifts of 100–500-meV in the calibrated NFET and PFET devices, respectively. DFV follows the Pelgrom law. When device shrinks,
$\sigma _{V_{\text {t}}}$
due to DFV will increase inversely proportional to the square root of channel area. Furthermore, as a new source of variability, DFV is compared with metal grain granularity (MGG), random dopant fluctuation (RDF), and oxide thickness variation (OTV) using the statistical impedance field method (sIFM) simulation technique. The results show that DFV contributes 10% (NFET) and 25% (PFET) to the overall variation when the dipole-induced potential shifts are set at 300 meV, indicating that DFV is a significant contributor to device variability with importance second only to MGG.