A single nano-void precisely positioned in SiO2/Si substrate by focused helium ion beam technique

We report on the formation of a single nano-void, precisely positioned in SiO2/Si, using He-ion beam technique. The in-plane position of the void can be achieved by the direct writing capability of the He-ion beam system. While the depth and size of void are able to be determined by the acceleration voltage and dosage of the He+-ions, respectively. The as-written sample shows an ellipsoidal shape amorphous region in Si. Thermal treatments aggregate He-vacancy complexes and He bubble defects to form a void in the central of the region. At the same time, recrystallization starts from the boundary between the amorphous and crystal Si. Through HAADF imaging, EDX scanning profile and SEM imaging, we show the existence of a nano-void at a predicted depth. For the sample annealed at 825 °C, we observed a single void formed by {111} facets.