HIGH-FIELD BREAKDOWN IN THIN OXIDES GROWN IN N2O AMBIENT

We report a detailed study of time-dependent dielectric breakdown (TDD B) in N2O-grown thin (47-120 angstrom) oxides. A significant degradati on in breakdown properties (such as charge-to-breakdown, breakdown fie ld) was observed in N2O oxides with increasing oxide growth temperatur e; a strikingly different dependence than that in pure oxides. A physi cal model based on undulations at the Si/SiO2 interface is discussed t o account for the degradation of breakdown properties for higher N2O o xidation temperature. Accelerated breakdown in N2O oxides for higher o perating temperatures and higher oxide fields as well as thickness dep endence of TDDB are studied under both polarities of injection. These dependencies are similar to the reported data on pure oxides. Breakdow n under unipolar and bipolar stress in N2O oxides is compared with dc breakdown. Unlike the case of pure oxides, an asymmetric improvement i n time-to-breakdown under positive versus negative gate unipolar stres s is observed, which is attributed to charge detrapping behavior in N2 O oxides. A dramatic reduction in time-to-breakdown of N2O oxide is ob served under bipolar stress when the thickness is scaled below 60 angs trom. A physical model, based on the thickness dependence of trapped h ole centroid, is suggested to explain this behavior. Overall, our resu lts indicate that N2O oxides are expected to show improved breakdown p roperties than pure SiO2 Over a wide range of operating temperatures, electric fields, oxide thicknesses, as well as under ac stress.