Polyoxides grown on n/sup +/ polysilicon

The polarity asymmetry on the electrical characteristics of the oxides grown on n/sup +/ polysilicon (polyoxides) was investigated in terms of the oxidation process, the doping level of the lower polysilicon layer, the oxidation temperature and the oxide thickness. It was found that the thin polyoxide prepared by using a low-temperature wafer loading and N/sub 2/ pre-annealing process, has a smoother polyoxide/polysilicon interface and exhibits a lower oxide tunneling current, a higher dielectric breakdown field when the top electrode is positively biased, a lower electron trapping rate and a larger charge-to-breakdown than does the normal polyoxide. The polarity asymmetry is also strongly dependent on the doping level of the lower polysilicon layer, the oxidation temperature and the oxide thickness. It was found that only the thinner polyoxides (/spl les/240 /spl Aring/) grown on the heavily-doped polysilicon film (30 /spl Omega//sq) by using the higher-temperature oxidation process (/spl ges/950/spl deg/C) conduct a less oxide tunneling current when the top electrode is positively biased.