Toward two-dimensional self-organization of nanostructures using wafer bonding and nanopatterned silicon surfaces

The structure of ultrathin silicon layers obtained by molecular hydrophobic bonding is investigated. The twist and tilt angles between the two crystals are accurately controlled. The buried Si|Si interface is observed by transmission electron microscopy and by grazing incidence X-ray techniques. For low twist angle values (ψ<5°) plane view observations reveal well-defined dislocation networks. Cross-section observations give evidence that the dislocation networks are localized at the bonding interfacial plane with no threading dislocation. Grazing incidence small angle X-ray scattering measurements confirm the good quality of the bonding interface as well as the quality of the dislocation networks. Grazing incidence X-ray diffraction is also used and shows the long-range order of the periodic strain field in the silicon layer. It shows, especially, the interaction between the dislocations. X-ray reflectivity was employed and estimated that the interfacial thickness (i.e., thickness of the bonding) lower than 1 nm decreases when the twist angle increases. The nanopatterned surface is then investigated by scanning tunneling microscopy and X-ray methods. To validate these substrates for long-range order self-organization, the growth of Si and Ge quantum dots is finally achieved.