The bottom oxide was found to play an important role on the integrity of interpolysilicon ultrathin oxide/nitride/oxide (ONO) films. Natural oxides grown on phosphorus‐doped polysilicon by diffusion from POCl 3 source contain defects and weak spots, which degrade the integrity of ONO films grown on these. On in situ phosphorus‐doped LPCVD polysilicon, defect‐free oxides can be obtained and introduce much better yield in ONO films. Dielectric strength measurement by voltage ramping method cannot separate this difference of integrity. We were able to discriminate this difference only by time dependent dielectric breakdown measurement in which negative voltage was applied to the upper polysilicon. The intrinsic wearout phenomena of ONO films, which have been observed on single‐crystal silicon surfaces, and depend only on the thicknesses of bottom oxide, nitride, and top oxide, were observed also on polysilicon if the bottom oxide has grown on in situ phosphorus‐doped LPCVD polysilicon.
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Naito et al. (1990) studied this question.
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