Interface-trap building rates in wet and dry oxides

The time-dependent buildup of radiation-induced interface-trap charge was characterized in polysilicon gate MOS transistors with wet and dry gate oxides with thicknesses varying from ~20 to ~100 nm. The buildup was characterized in terms of the time required to achieve 50% of the saturated density of interface traps. For both types of oxides, an approximate t_ox^0.4 dependence of the interface-trap buildup rate is observed following +1 MV/cm irradiation and anneal, and an approximate t_ox^1.7 dependence is observed following -1 MV/cm irradiation and +1 MV/cm anneal. The fact that these thickness dependences differ from recent literature reports suggests that the manner in which hydrogen is incorporated in the oxide during processing may play a key role in determining whether H⁺ is released in the bulk of the oxide, or near an interface. At any given oxide thickness and irradiation condition, the buildup rate was found to be faster in the dry gate oxides than the wet gate oxides