Three-dimensional nanostructures fabricated by stacking pre-patterned monocrystalline silicon nanomembranes

Abstract

This thesis considers the viability of nanomembrane handling and stacking approaches to enable the fabrication of three-dimensional (3D) nano-structured materials. Sequentially stacking previously-patterned membranes to build up 3D nanostructures, e.g. photonic crystals, is a powerful technique that decouples serial patterning processes from 3D assembly, allows the incorporation of photonic devices into the material and facilitates in-process error inspection. A technique identified to address the fundamental problems with stacking disjoined membranes, i.e. those populated with photonic devices, using water-based approaches was an outgrowth of methods to fabricate, handle and stack their connected counterparts. Initially, connected nanomembranes patterned in a thin layer of silicon on glass were released in hydrofluoric acid where surface tension caused them to float flat. Their fragility inspired novel handling and position manipulation techniques for layer-to-layer alignment. While exploiting surface tension allowed membranes to be stacked using water, drifting precluded precision placement. Although carrier substrates held them stationary, the membranes leaked water before Van-der Waals adhesion was overcome. To address such issues a novel method is introduced whereby a sublimable glue affixes membranes to a glass carrier, which is placed membrane-side down onto a receiving substrate and the glue is vaporized to detach the membranes, leaving them bound to the previous layer.