Impact of Oxide Thickness Fluctuation and Local Gate Depletion on Threshold Voltage Variation in Metal–Oxide–Semiconductor Field-Effect Transistors

概要

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Threshold voltage ($V_{\text{th}}$) variations induced by oxide thickness fluctuation (OTF) and local gate depletion (LGD) in metal–oxide–semiconductor field-effect transistors (MOSFETs) are studied using classical three-dimensional (3D) drift-diffusion (DD) simulations. The models for both OTF and LGD are based on transmission electron microscopy (TEM) observations. OTF is generated by random roughness steps at a SiO2/Si interface and LGD is generated by the random size and position of grains in a polycrystalline silicon (poly-Si) gate. The impact of both models on $V_{\text{th}}$ variation and its distribution are investigated and compared with measured data. The Takeuchi coefficient $B_{\text{VT}}$ is used to analyze $V_{\text{th}}$ variation. It is found that, although both OTF and LGD have an impact on $V_{\text{th}}$ variation, their influences are small in terms of $B_{\text{VT}}$ value, the dependence of $B_{\text{VT}}$ on $N_{\text{a}}$ and $T_{\text{inv}}$, and the $V_{\text{th}}$ distribution.
2009-06-25