Nonplanar oxidation and reduction of oxide leakage currents at silicon corners by rounding-off oxidation

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Abstract
We report that, based on the curvature radius at the convex corner of a trenched Si surface and electric field intensification, sacrificial thermal oxidation before gate oxide formation is very effective to round off the convex corner. We call it a rounding-off oxidation. From a simple one-dimensional model that considers both stress generation during Si oxidation and Stress relaxation by oxide viscous flow, it is foreseen that oxidation in a diluted oxidizing ambient and/or at a higher oxidation temperature reduces the stress in the oxide films. Experimentally, we report that the rounding-off oxidation with the above condition effectively rounds off the convex Si corner and decreases the thin gate oxide leakage currents and that the addition of a few percent of H2O to the dry oxygen rounding,off oxidation ambient is also effective. The relation between the sacrificial rounding-off oxidation and the time-dependent dielectric breakdown of thin gate oxides formed at the convex corner is also shown.

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