Technical Papers and Presentations

With the scaling of semiconductor devices into the nanometer regime, short channel effects are an ever-present issue. Among these effects are threshold voltage variation with channel length, reduced output resistance, punch-through and hot-electron degradation. The effect of constant-field scaling on a FIBMOS (focused-ion-beam metal-oxide-semiconductor) device compared to the conventional MOSFET (metal-oxide-semiconductor field-effect transistor) is studied in this paper. Using the COMSOL Multiphysics^® simulation software's Semiconductor Module, the 2D models of the devices are designed. The transistors are constructed using silicon, and regions with different doping concentrations have been implemented. A narrow P+ region with higher doping concentration than the substrate is implanted next to the source region, using COMSOL Multiphysics^® Doping Models, to emulate an asymmetric device structure that is made using the Focused-Ion-Beam technique. The effects on mobility of the carriers due to lattice vibrations, ionized impurity ions, carrier concentrations, surface effects and presence of large electric fields have been addressed by incorporating Mobility Models into the simulator. Recombination of the carriers has been considered by implementing the Trap Assisted Recombination Model. The simulation is conducted on a conventional MOSFET as well as a FIBMOS transistor for 122.5-nm, 175-nm, 245-nm, and 350-nm channel-length devices. A parametric sweep is used to scale the devices while running the simulations. Two different user-controlled meshes are generated according to the need of the simulations, and stationary analyses are performed using modified solver settings in order to facilitate running the simulation with the mobility models employed. An investigation is conducted on threshold voltage stability upon channel length variation, output resistance, electrical field inside the channel, and sub-threshold conduction to see if the FIBMOS demonstrates the characteristics of an ideal transistor compared to the conventional MOSFET. The simulations show that the FIBMOS device demonstrates greater threshold voltage stability upon channel length variation, improved output resistance, greater resistance to the punch-through effect, and reduced hot electron degradation.