Model for Si–SiO2 interface state formation during irradiation and during post-irradiation exposure to hydrogen environment

When the oxide of a previously x-ray irradiated metal–oxide–semiconductor field-effect transistor is exposed to a hydrogen environment at room temperature the number of interface traps is observed to double, and the number of fixed oxide traps to decrease by a similar amount. From an analysis of this post-irradiation behavior we derive a model for the formation of interface states during and immediately after irradiation. In this model holes formed in the oxide during the irradiation split ≡SiH bonds in the oxide to form atomic hydrogen and ≡Si+. At room temperature the atomic hydrogen quickly dimerize to form H2. The H2 is then cracked by the ≡Si+ to form H+. Each H+ is transported to the interface, where it forms an interface state. This model also explains the results of a recent experiment which had seemed to indicate that no H+ was formed in the oxide as a result of irradiation.