Transient-enhanced Si diffusion on natural-oxide-covered Si(0 0 1) nano-structures during vacuum annealing

The morphology of annealed patterned Si(0 0 1) wire templates was studied by several techniques. We found an enormous Si-mass transport on the Si surface at usual oxide desorption temperatures around 900°C under UHV conditions. Heat treatment of 5 min transforms the initially rectangular wire profiles with a height of 300 nm to flat (<100 nm) and faceted triangular ridges exhibiting thermodynamically preferred {1 1 1} - and {3 1 1} -facets. It was found that the natural SiO ₂ on the predefined wire pattern must be responsible for the degradation of the wire structure. Removing the SiO ₂ layer from the Si wires ex situ with an HF dip preserves the rectangular structures during high-temperature annealing. The Si-SiO ₂ interface was investigated with high-resolution transmission electron microscopy to image the Si wire surface and the natural oxide layer in detail.