Physically based simulation of fully depleted SOI MOS transistors at nanometer gate lengths
Coupled process and device simulation has been applied to investigate the physical processes which determine the performance and scaling properties of fully depleted thin-silicon-body SOI based (FDSOI) NMOS transistors at gate lengths of 40 nm and below. A comparison of simulation results with measurements of electrical characteristics of the FDSOI NMOS transistors showed that the electrical performance of such transistors can only be reproduced by simulation, if contact resistances, ballistic electron transport, quantum mechanical depletion of the electrons near the gate dielectric, and mechanical stress are accounted for. The mechanical stress in thin-silicon-body SOI transistors is simulated as a result of two silicidation processes: the source/drain contact CoSi2 silicidation and NiSi gate silicidation. The resulting stress in the silicon channel at the end of processing is tensile along the gate length, non-uniform and reaches maximum values in excess of 1 GPa. The simulations show that mechanical stress as well as the contact resistances increase for scaled FDSOI transistors, therefore a careful optimization of mechanical stress and an engineering of contact resistances are mandatory for scaled FDSOI devices.