Intrinsic threshold voltage fluctuations in decanano MOSFETs due to local oxide thickness variations

Intrinsic threshold voltage fluctuations introduced by local oxide thickness variations (OTVs) in deep submicrometer (decanano) MOSFETs are studied using three-dimensional (3-D) numerical simulations on a statistical scale. Quantum mechanical effects are included in the simulations employing the density gradient (DG) formalism. The random Si/SiO2 and gate/SiO2 interfaces are generated from a power spectrum corresponding to the autocorrelation function of the interface roughness. The impact on the intrinsic threshold voltage fluctuations of both the parameters used to reconstruct the random interface and the MOSFET design parameters are studied using carefully designed simulation experiments. The simulations show that intrinsic threshold voltage fluctuations induced by local OTV become significant when the dimensions of the devices become comparable to the correlation length of the interface. In MOSFETs with characteristic dimensions below 30 nm and conventional architecture, they are comparable to the threshold voltage fluctuations introduced by random discrete dopants.