The structure of a thin (10 nm) oxide, grown in micron-sized trenches in silicon, has been studied by high resolution electron microscopy (HREM). The trenches were produced in {100} wafers by dry etching, and have {110} sidewalls and {100} bottom surfaces. Oxidation was carried out at 1!25~ by rapid thermal annealing in pure, dry 02 to produce a nominal 10 nm oxide on the top wafer surface. It is found that the oxide is largely smooth and continuous, with minimal Si-SiQ protrusions. However, the oxide thickness varies significantly around the trench, being thickest at the {110} sidewalls and thinnest in the inner, concave corners. In addition the latter are distinctly faceted on {111} and {311} planes. It is thought that crystallography plays an important role in the variation of trench structure after oxidation.

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