Effects of quantization on random telegraph signals observed in deep-submicron MOSFETs

Random telegraph signals (RTS) have been investigated in the drain to source voltage of W-eff x L-eff = 1.37 x 0.17 mum(2) medium-doped drain (MDD) n-type MOSFETs. The emission (tau (e)) and capture (tau (c)) times of the probed trap were studied as a function of gate voltage as well as substrate voltage. The small size and high doping density of the n-MOSFETs studied create a strong electric field in the MOSFET inversion layer, which makes the surface conduction band split into discrete energy levels. Therefore, modified expressions of tau (e) and tau (c) including the influence of bulk bias (V-SB), which changes the degree of quantization, are presented. The trap position in the oxide with respect to the Si-SiO2 interface, and the trap energy, were calculated from the gate voltage dependence of the emission and capture times under different bulk bias conditions. The behavior of the emission and capture times predicted by the two-dimensional (2D) surface quantization effects is in qualitative agreement with the experimental results. The RTS amplitude (DeltaV(DS)/V-DS) shows a positive dependence on V-SB. The coefficient alpha fbr screened oxide charge scattering was calculated at different gate voltages and bulk bias from the RTS amplitude. In addition, the theoretical calculation of the scattering coefficient alpha, using a 2D surface mobility fluctuation model, was presented, which shows a good agreement with the experimental data. (C) 2000 Elsevier Science Ltd. All rights reserved.