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

Abstract

Threshold voltage (Vth) 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 Vth variation and its distribution are investigated and compared with measured data. The Takeuchi coefficient BVT is used to analyze Vth variation. It is found that, although both OTF and LGD have an impact on Vth variation, their influences are small in terms of BVT value, the dependence of BVT on Na and Tinv, and the Vth distribution.