Field dependence of interface-trap buildup in polysilicon and metal gate MOS devices

The electric field dependence of radiation-induced oxide- and interface-trap charge (ΔV_ot and ΔV _it) generation for polysilicon- and metal-gate MOS transistors is investigated at electric fields (E_ox) from -4.2 MV/cm to +4.7 MV/cm. If electron-hole recombination effects are taken into account, the absolute value of ΔV_ot and the saturated value of ΔV_it for both polysilicon- and metal-gate transistors are shown to follow an approximate E^-1/2 field dependence for E _ox⩾0.4 MV/cm. An E^-1/2 dependence for the saturated value of ΔV_it was also observed for negative-bias irradiation followed by a constant positive-bias anneal. The E^-1/2 field dependence observed suggests that the total number of interface traps created in these devices may be determined by hole trapping near the Si/SiO₂ interface for positive-bias irradiation or near the gate/SiO₂ interface for negative bias irradiation, though H⁺ drift remains the likely rate-limiting step in the process. Based on these results, a hole-trapping/hydrogen transport model-involving hole trapping and subsequent near-interfacial H⁺ release, transport, and reaction at the interface-is proposed as a possible explanation of ΔV_it buildup in these polysilicon- and metal-gate transistors