The Effect of Mobile Sodium Ions on Field Enhancement Dielectric Breakdown in SiO[sub 2] Films on Silicon

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Abstract
The presence of mobile sodium ions in films, thermally grown on silicon, can lead to time‐dependent conduction and subsequent dielectric breakdown. When this occurs, it will be shown that anomalously high (ten orders of magnitude) electronic currents can result, presumably because of a modification of the shape of the injecting barrier, due to the high electric field created by the presence of the uncompensated positive charge. The time required to break down the film under an applied field was found to approximate the empirically known Peek's law relationship, i.e., . Moreover, it will be demonstrated that field enhancement in the oxide due to space charge effects provides the fundamental breakdown mechanism. Capacitance ‐voltage measurements of the silicon flatband voltage were used to determine the internally created field, and thereby to demonstrate that breakdown occurred when the total field reached the breakdown strength of the film. It will be seen that the limiting time before breakdown, with sodium‐contaminated samples, correlates with the kinetics of ionic motion, e.g., it exhibits the same activation energy and varies roughly as the square of the oxide thickness. The other statistical variations in breakdown times can be quantitatively attributed to defects present in the starting oxide films.

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