Reliability of SiO2 Gate Dielectric with Semi-Recessed Oxide Isolation

This paper reports the results of a study to minimize defects in the gate oxide and in the single crystal substrate of semi-recessed oxide (Semi-ROX) structures. It is shown that both an increase in oxidation mask thickness and a decrease in wet field oxidation temperature markedly reduce the incidence of low voltage breakdown in the gate oxide. Microscopic studies of samples which exhibited low voltage breakdown showed that the Si
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oxidation mask had failed to protect the surface of the region in which the gate oxide was grown. Semi-ROX processing also exhibited edge breakdown, most likely due to the Kooi effect (nitrided Si surface). The use of a thicker “pad” oxide and a decrease in the wet field oxide thickness were beneficial in reducing the magnitude of degradation in gate breakdown due to this edge effect.