HIGH-FIELD BREAKDOWN IN THIN OXIDES GROWN IN N2O AMBIENT

Abstract

We report a detailed study of time-dependent dielectric breakdown (TDDB) in N2O-grown thin (47-120 angstrom) oxides. A significant degradation in breakdown properties (such as charge-to-breakdown, breakdown field) was observed in N2O oxides with increasing oxide growth temperature; a strikingly different dependence than that in pure oxides. A physical model based on undulations at the Si/SiO2 interface is discussed to account for the degradation of breakdown properties for higher N2O oxidation temperature. Accelerated breakdown in N2O oxides for higher operating temperatures and higher oxide fields as well as thickness dependence of TDDB are studied under both polarities of injection. These dependencies are similar to the reported data on pure oxides. Breakdown under unipolar and bipolar stress in N2O oxides is compared with dc breakdown. Unlike the case of pure oxides, an asymmetric improvement in time-to-breakdown under positive versus negative gate unipolar stress is observed, which is attributed to charge detrapping behavior in N2O oxides. A dramatic reduction in time-to-breakdown of N2O oxide is observed under bipolar stress when the thickness is scaled below 60 angstrom. A physical model, based on the thickness dependence of trapped hole centroid, is suggested to explain this behavior. Overall, our results indicate that N2O oxides are expected to show improved breakdown properties than pure SiO2 Over a wide range of operating temperatures, electric fields, oxide thicknesses, as well as under ac stress.