Effect of Source/Drain Doping Gradient on Threshold Voltage Variation in Double-Gate Fin Field Effect Transistors as Determined by Discrete Random Doping

Abstract

We present a numerical simulation and physical analysis of how a single dopant in the channel region effects the variation of threshold voltage ΔVth in highly scaled (gate length = 16 nm) and undoped double-gate fin field effect transistors. The presence of a single contaminant dopant in an undoped channel with an abrupt source/drain (S/D) doping gradient can cause a severe change in ΔVth (140 mV owing to a single acceptor; 100 mV owing to a single donor). To effectively suppress this severe variation, we suggest S/D doping gradient engineering to make the lateral straggle of S/D doping (σS/D) larger than 2 nm to minimize ΔVth. The distribution of Vth is also estimated by three-dimensional simulation using the position of the dopant.