Electrical conduction and breakdown in oxides of polycrystalline silicon and their correlation with interface texture

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Abstract
The electrical properties of oxidized polysilicon (poly‐oxide) were measured for samples of various thicknesses, grown from polysilicon which had been doped at temperatures of 900–1000 °C, and oxidized in steam or dry oxygen at temperatures of 850–1050 °C. The electrical conduction can be explained in terms of Fowler‐Nordheim tunneling at sites of roughness of the polysilicon/poly‐oxide interface, and in terms of deep electron traps near that interface, in agreement with previously published results. We have found additional evidence for such electron traps. We find that higher doping and oxidation temperatures tend to yield oxides with higher breakdown fields, although there is considerable variation among different sets of samples. We observe no significant differences in the polysilicon/poly‐oxide interface texture by cross‐sectional transmission electron microscopy. However, we find a strong correlation between the applied field necessary for a significant leakage current through the poly‐oxide and the applied field which causes breakdown. This finding supports the model that both the leakage current and the oxide breakdown are caused by locally enhanced electric fields within the poly‐oxide. The concepts of an enhanced local electric field due to polysilicon/poly‐oxide interface roughness and of the formation of electron traps at regions of strong local electric field are used to model the experimentally observed conduction and breakdown processes and to propose additional effects. The electric field enhancement due to a hemispherical protuberance at the interface is calculated analytically.