Abstract A comparison between overlapping and non-overlapping polyoxide capacitors shows that overlapping edge results in high tunnelling currents at moderate electric fields. Calculations of the local electric field distribution show that the shape of the polysilicon top corner is very important. Sharp top corners result in high electric field peaks. Shaping of this corner, by sloping and/or rounding, has been shown to reduce the peak to an acceptable height. This paper presents a practical implementation of this shaping, using an isotropic NF3 plasma etch resulting in an appreciable current reduction. Next to this top corner, some electric field calculation in the bottom region of the edge have also been performed, showing the importance of the polysilicon shape.
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