Effect of Gate Materials on Generation of Interface State by Hot-Carrier Injection

Abstract

The effect of gate materials on hot-carrier degradation, especially on the generation of the interface state, is investigated. The generation of the interface state in n-channel metal-oxide-semiconductor field-effect transistors (NMOSFET's) by drain avalanche hot-carrier (DAHC) injection is independent of the gate material. On the other hand, the generation of the interface state in p-channel MOSFET's (PMOSFET's) by DAHC injection is greatly dependent on the gate material but almost independent of the channel doping profile, in other words, a surface- or buried-channel device. The increase in interface state density (ΔDit) in tungsten (W)-gate PMOSFET's is much larger than that of polycide-gate devices. In order to verify the effect of carrier species injected into SiO2, electrons were injected from the substrate into the gate electrode by two methods: Fowler-Nordheim injection and hot-electron injection from the forward biased p-n junction injector. The large ΔDit in W-gate devices is observed in both methods. It is confirmed that the large ΔDit in W-gate PMOSFET's stressed by DAHC injection is caused by the injection of electrons into SiO2. These phenomena are considered to occur due to the difference of hole injection from the gate into SiO2, excited at the gate by electron injection, between gate materials.