INTERFACE-TRAP BUILDUP 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 approximately 20 to approximately 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 dependence 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. It is suggested that the difference in buildup rates between the wet and dry oxides could be due to differences in the mobility of H+ in wet versus dry gate oxides, or to different spatial hole-trap distributions in the wet versus dry gate oxides.