Influence of Doping Gradient near a Channel End on Parasitic Series Resistance of Thin-Film Fully-Depleted Metal–Oxide–Semiconductor Field-Effect Transistors

Abstract

We experimentally investigated parasitic series resistance in thin-film fully-depleted (FD) metal–oxide–semiconductor field-effect transistors (MOSFETs) built on thin-film silicon-on-insulator (SOI) substrates. We clarified that the resistance near a channel end in FD SOI MOSFETs plays a major role in the parasitic resistance, Rpara, and that it becomes more significant in devices with a tungsten-covered source and drain. The resistance near the channel end is largely affected by the doping concentration and gradient, and it decreases as a junction becomes steeper. The process condition in source and drain formation, such as dopants implantation energy, rapid thermal annealing largely influences the lateral diffusion of dopants, and thus the steepness of the junction. The SOI thickness and argon-ion implantation for suppression of floating body effects also affect the lateral diffusion and thereby the Rpara of FD SOI MOSFETs. The argon-ion implantation after a formation of source and drain can induce an anomalous lateral diffusion of dopants, which might increase the Rpara. Thinner SOI film can suppress the lateral diffusion, and therefore might be effective for decreasing the Rpara.