Submicrometer MOSFET Structure for Minimizing Hot-Carrier Generation

This paper reports on investigation of channel hot-carrier generation for various device structures. The dependence of channel hot-carrier generation on MOSFET structure are characterized by measuring the gate current and the substrate current as low as on the order of 10^-15 A. The measured gate current due to hot-electron injection into the oxide is modeled numerically as thermionic emission from heated electron gas over the Si-SiO₂ energy barrier. The substrate current due to hot-hole injection into the substrate is also modeled analytically. On the basis of the experiments and analyses, two device structures are proposed for minimizing hot-carrier generation and associated problems in submicrometer MOSFET: a graded drain junction structure and an offset gate structure. The proposed device structures provide remarkable improvements, raising by 2 V the highest applicable voltages as limited by hot-electron injection, as well as raising by 1-3 V the drain sustaining voltages as determined by the substrate hot-hole current. The influence of electron-beam radiation on the gate oxide is also discussed in relation to the trapping of hot electrons.