Decomposition kinetics of silicon oxide layers on silicon substrates during annealing in vacuum

Thermal decomposition of silicon oxide layers (5–20 nm in thickness) on silicon substrates has been investigated by scanning electron microscopy and atomic force microscopy. The obtained microscopic images reveal that silicon atoms necessary for the oxide decomposition are supplied to the thick oxide layer at the sidewall of voids, which are formed by inhomogeneous oxide decomposition. We also show that the shape of the voids depends on the surface orientation of the silicon substrates, and silicon nanostructures are formed inside the voids owing to annealing/cooling cycles. The detailed observation of the silicon nanostructures indicates that one of the triggers of initial void formation is the difference in thermal expansion of silicon and silicon oxide.