Low-density oxide grown thermally on sidewall of Si nanopillars

Diffusion inhibition of the oxidant in the oxide, developed from thermal oxidation of the two-dimensional Si planar surface, has been considered to be the mechanism of self-limiting oxidation of Si nanopillars by many groups over a long period. However, in this work, we found that oxide grown thermally on the sidewall of Si nanopillars has lower density compared to that on a two-dimensional planar bottom surface oxidized under the same conditions. The oxidant diffuses faster in lower density SiO₂, which means that the oxidant diffusion inhibition model is insufficient for explaining the self-limiting oxidation of Si nanopillars. A simple model is proposed to explain the formation mechanism of low-density oxide grown thermally on the sidewall of Si nanopillars. This work contributes in intrinsically understanding and precisely controlling the oxidation of Si nanopillars for future device fabrications.