Transport properties of thermal oxide films grown on polycrystalline silicon—Modeling and experiments

A theoretical model considering the effects of Fowler-Nordheim tunneling, image-force lowering, first-order trapping kinetics, impact ionization, and asperity-induced field enhancement has been developed to investigate the ramp-voltage-stressed I-V characteristics of the oxide films thermally grown on the polycrystalline silicon. From the ramp-voltage-stressed I-V measurements, the important physical parameters such as average field-enhancement factor, effective total trapping density, trap capture cross section, recombination capture cross section, and dielectric breakdown field can be extracted. Under a ramp voltage stress, it is shown that the serious asperity effect can lead to a larger leakage current and a weaker dielectric breakdown field, but the serious trapping effect may reduce the leakage current and enlarge the dielectric breakdown field. Moreover, dry O2oxidation at a higher temperature and steam oxidation at a lower temperature can result in a better quality poly-oxide because the asperity-induced field enhancement is weakened and the electron trapping effect is slightly increased. Besides, high-temperature dry O2oxidation can result in a smaller asperity effect as compared with steam oxidation, and the quality of the poly-oxide is deteriorated when the poly-Si substrate is heavily doped because the asperity effect is enhanced.