Significant electron trapping has been observed in thermally grown interlevel oxide on polycrystalline silicon (poly‐Si) structure. The trapped charges were concentrated about 50Å away from the interface between the underlying poly‐Si and the oxide grown upon it. The mechanism responsible for the high density of electron traps appears to be out‐diffusion of phosphorus from poly‐Si. Much less charge trapping was observed when poly‐Si was covered by thermal oxide plus a layer of silicon nitride. The dual dielectric structure also displayed a higher oxide breakdown field strength.

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