A characterization model for constant current stressed voltage-time characteristics of thin thermal oxides grown on silicon substrates

Abstract

The constant-current-stressed voltage-time (V-t) characteristics of the thin SiO2 films thermally grown on the silicon substrate has been analyzed by using a theoretical model which includes the effects of dynamic trapping (i.e., electron trapping and detrapping), positive charge generation, weak spots, and robust area. The experimental methods have been developed to extract the physical parameters concerned with electron trapping and detrapping as well as positive charge generation. The time-dependent dielectric breakdown of the intrinsic thin SiO2 films under a constant current stress can be predicted through a criterion which assumes that the positive ions generated from impact ionization are aggregated near the interface between SiO2 and Si within the weak spots. Computer simulations using the proposed model indicate that the life of the intrinsic thin SiO2 film can be elongated if the trapping effect is less severe, the trapped electron centroid is closer to the anode electrode, the generated positive ions have a smaller recombination capture cross section, and the weak spots have a larger area ratio with respect to the total area. Besides, experiments have been performed to observe the effects of electron trapping and positive charge generation. Furthermore, the physical parameters of the poly-Si and Al-gate thin SiO2 films have been obtained under different constant current densities and the theoretical simulations have been performed. Good agreement between the experimental data and the theoretical simulations suggests that the proposed model can be used as a computer-aided-design (CAD) tool to predict the life of the intrinsic thin SiO2 films.