ELECTRICAL BREAKDOWN INDUCED BY SILICON-NITRIDE ROUGHNESS IN THIN OXIDE-NITRIDE-OXIDE FILMS

The time-dependent dielectric breakdown (TDDB) characteristics of thin oxid-nitride-oxide (ONO) films containing 4 nm of Si3N4 were found to be exclusively determined by statistical thickness fluctuations of th e Si3N4 layer. A two-parameter statistical model describes this roughn ess and explains experimental TDDB data. A simple growth model combine d with the statistical model reduces the number of parameters to one. It is consistent with TDDB data and is in quantitative agreement with transmission electron microscopy and x-ray photoelectron spectroscopy data and is able to explain the origin of the roughness. On an ONO wit h a 4 nm Si3N4 layer and an area of 8 cm(2)-corresponding to the total storage area of a 256 Mbit dynamic random access memory-the thinnest point in the Si3N4 can be expected to be below 10 Angstrom. So elimina ting the Si3N4 roughness would bring a drastic improvement in reliabil ity. (C) 1996 American Institute of Physics.