Properties of stacked dielectric films composed of SiO2/Si3N4/SiO2

Dielectric films composed of silicon oxide-nitride-oxide (ONO) structure have been grown over a polycrystalline silicon phosphorous-doped substrate. The films with a total thickness of about 30 nm have been obtained by two different deposition techniques of the top-oxide layer i.e. thermal oxidation of the nitride layers and low pressure chemical vapour deposition, while the bottom oxide and the nitride layer were obtained by thermal oxidation and low pressure chemical vapour deposition, respectively. The chemical composition was measured by XPS Auger parameter technique while the thickness of the deposited layers was determined by the X-ray reflectivity method and compared with the measurements performed on transmission electron microscopy cross-section images. The influence of the layer composition and thickness on the electrical properties of the whole film, used as dielectric layer of a capacitor with doped polycrystalline silicon as electrodes, have been investigated by measuring current as a function of voltage to study the mechanisms which contribute to an increase of the leakage current with increasing applied voltage. Furthermore, electrical erasable programmable read-only flash memory devices built using these dielectric layers in the Boating gate structure have been measured for 'data retention loss' after thermal stress. The results give a complete picture on the role of the two topmost layers of the ONO structure towards the electrical behaviour. (C) 1999 Elsevier Science B.V. All rights reserved.