NEW HOT-CARRIER-INDUCED DEGRADATION PHENOMENA IN HALF-MICROMETER MOS TRANSISTORS.

The degradation magnitude is one to two orders larger than that of the severest stress condition ever reported, and increases rapidly with decreasing gate length. This phenomenon limits the applicable voltage for 0. 5- mu m MOSFETs. The mechanism of this large degradation has been determined using experimental data and simulation results. The large degradation is due to the highly efficient injection of hot electrons into the gate oxide. The degradation magnitude has a positive strong correlation with gate currents instead of substrate currents over a wide range of bias voltage. From these results and two-dimensional two-carrier device simulations, it has been determined that the large degradation is caused by the large impact ionization just at the Si/SiO//2 interface in the source high-resistivity region (source impact), and by the high electric field enhancing the hot-electron injection of hot electrons into the gate oxide, resulting in the large degradation. Moreover, the magnitude of the new degradation mode increases rapidly with decreasing the gate length to 0. 5 mu m. So, it becomes extremely important to suppress this degradation mode in the design of reliable 0. 5- mu m MOSFETs. Some methods of suppressing this degradation are presented and discussed.