Pattern-dependent oxidation (PADOX) of silicon nanostructures fabricated on silicon-on-insulator (SOI) substrates is simulated. The volume expansion due to silicon oxidation is treated as a dilational strain, and the strain is applied to a transition region in which silicon is converted to oxide. In addition, the silicon oxide and transition layer are treated as viscoelastic solids. The simulation results indicate that the oxidation-induced compressive stress reduces the oxide viscosity by a few orders of magnitude and that rounded silicon shapes after oxidation are mainly caused by this reduction of oxide viscosity. In addition, we examined the relation between the oxidation-induced stress and the oxidation from below, and showed that the effect of the stress on the oxidation reaction rate affects the silicon shapes after oxidation.
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