The Effect of Hot-Carrier and Fowler-Nordheim Injection on VLSI Mosfet at Room and Cryogenic Temperatures.

The influence of hot-carrier injection (HCI) on the performance of MOS transistors has been studied extensively during the last decade due to its effects that lead to long-term reliability problems and pose a serious limitation on the feature size reduction. In parallel with the reduction in channel length, the gate oxide of VLSI MOSFET's is also getting thinner and thinner. The reliability of the thin gate oxides has become an important issue due to the effect of time-dependent di-electric breakdown (TDDB). This failure mechanism is mostly resulting from the charge trapping by Fowler-Nordheim(F-N) injection. The main goal of this PhD dissertation research is to improve the understanding of the mechanism of these two major reliability problems in modern VLSI MOSFET's. The impact of HCI and F-N injection on circuit parameters and the link between the degradation in device characteristics and circuit parameters is also studied in order to evaluate and link the device and circuit level reliability. A strong correlation is observed between HCI and F-N injection. It is shown that a more heavily damaged oxide has a lower critical energy for hot-carrier injection to create an interface trap and a lower activation energy as well for Fowler-Nordheim injection to create a hole in the oxide. It is found that, in the stressed MOSFET's, the Hooge's parameter, which is directly proportional to the slow states, as determined from noise measurements, correlates with fast interface states determined from charge pumping and subthreshold swing measurements. This work also successfully demonstrates the feasibility of charge pumping technique down to freezeout regime in scaled VLSI MOSFET's. This observation enables us to study the exacerbated low temperature hot-carrier effect and the mechanism of charge pumping. Based on the low temperature charge pumping technique, generation-recombination (g-r) centers can be distinguished from traps in the interface states. By varying the pulse frequency and duty-cycle, we can determine not only the distribution of stress-induced g-r centers or traps within the bandgap but also the distribution for traps with various emission time constants. The device and circuit level HCI and F-N injection reliability is studied to obtain the link between the degradation in device characteristics and circuit parameters. The circuit parameters such as inverter propagation delay ( t_{P}), ring oscillator frequency (f_{OSC}), and voltage transfer characteristic (VTC) were measured and compared to the transistor parameters such as drain current, transconductance (g_{m}), threshold voltage (V_{t}). g_{m} degradation in a device is larger and about one order larger than the propagation delay degradation in an inverter for the same stress condition. Voltage transfer characteristics show larger improvement due to cooling for virgin inverters than for HC or F-N stressed inverters.