The gate oxide lifetime limited by `B-mode' stress induced leakagecurrent and the scaling limit of silicon dioxides in the direct tunnellingregime

Abstract

The scaling limit of the silicon dioxides as gate dielectrics isdiscussed from the viewpoint of the oxide lifetime. First, the definition ofthe `oxide lifetime' in the direct tunnelling regime has been studied, eventhough various studies report that soft breakdown (SBD) induces devicefailure. It is revealed that the previous studies overestimated the leakagecurrent after the SBD, i.e. the `B-mode' stress induced leakage current(B-mode SILC), and that the SBD stressed under typical device-operatingconditions never prevents the transistors from working well. Although hardbreakdown is expected to limit the oxide lifetime consequently, a new conceptof oxide lifetime limited by the chip-level off-leakage current, i.e. thestatistical effect of the B-mode SILC, has been proposed. The study on thestress voltage dependence of oxide lifetimes limited by these two factorsdemonstrates that the oxide lifetime under typical device-operating conditionsis limited by the B-mode SILC. Based on this concept, it has been clarifiedthat the oxide lifetime as a reliability issue does not limit the scaling downof silicon dioxides as the gate dielectrics in future devices.