Beam-tailored Catalyst Templates for Silicon Nanowire Synthesis

Motivation 1-dimensional nanostructures are considered among the most promising approaches for downscaling of microelectronic devices. Especially Si-nanowires (Si-NW) fulfill the necessity of technical compatibility with mainstream semiconductor technology. Their application in vertical transistor devices and in biosensors is envisioned. Although synthesis of Si-nanowires is already well examined, research has not yet succeeded in the controlled growth of epitaxial nanowires on predefined positions on non-flat surfaces. A specific alignment of the NW on the 3-dimensionally prestructured substrate is essential for application in a functional device. The positioning of metal nanoparticles acting as catalytic nucleation sites for Si-nanowires may offer a solution for this issue. Unfortunately conventional lithography is not applicable on 3-dimensionally prestructured substrates. Method In order to overcome the lithographic restrictions the fabrication of nanoparticle templates will be performed by a mask-less direct-write method. Electron-beam-induced deposition with a scanning electron microscope will yield locally confined deposition in the sub-50 nm range. Simultaneous introduction of up to 3 precursor gases will enable deposition of metal alloys. For synthesis of Si-NWs a dedicated LPCVD-reactor will be used. Si-NWs are synthesized by chemical vapor deposition following a catalysed vapor-liquid-solid mechanism. Project Plan Based on previous own research this work will address new challenges in 2 disciplines: - Fabrication of metal alloy templates on prestructured 3D substrates Electron beam induced deposition (EBID) is used to fabricate metal alloy nanoparticles by maskless direct-writing. Predefined patterns of metal alloy nanoparticles on planar and 3-dimensionally prestructured substrates will be fabricated as catalytic template for nanowire synthesis. - Synthesis of epitaxial silicon nanowires on predefined positions using catalytic nanoparticle templates The beam-tailored catalyst templates enable new opportunities in nanowire synthesis. On predefined positions epitaxial Si-nanowires will be grown by CVD from inorganic silicon precursors. The new approach enables synthesis of Si-nanowires on 3-dimensional prestructured substrates with arbitrarily oriented crystalline surfaces. The catalytic properties of various metals and alloys will be investigated. Relevance The unique combination of contemporary methods will break new ground scientifically by (i) the first EBID deposition of alloys and (ii) the accurate positioning of nanowires on non-flat surfaces. The EBID-deposition of alloys with controlled composition will enable to tailor catalysts with a suitable melting point enabling NW growth at moderate temperatures. The nanoparticle deposition on 3-dimensionally prestructured substrates will stimulate Si-NW growth on custom-designed templates. For the first time the positioning of NWs on specific locations of 3- dimensional substrates becomes possible. This enabling technique significantly improves the application potential of Si-NWs for functional device structures such as 1-dimensional electronic devices (nanowire transistor), sensitive biosensors and field emitter devices.

1-dimensional nanostructures are considered among the most promising approaches for downscaling of microelectronic devices. Especially Si-nanowires (Si-NW) fulfill the necessity of technical compatibility with mainstream semiconductor technology. Their application in vertical transistor devices and in biosensors is envisioned. Although synthesis of Si-nanowires is already well examined, research has not yet succeeded in the controlled growth of epitaxial nanowires on predefined positions on non-flat surfaces. A specific alignment of the NW on the 3-dimensionally prestructured substrate is essential for application in a functional device. The positioning of metal nanoparticles acting as catalytic nucleation sites for Si-nanowires may offer a solution for this issue. Unfortunately conventional lithography is not applicable on 3-dimensionally prestructured substrates. Method In order to overcome the lithographic restrictions the fabrication of nanoparticle templates will be performed by a mask-less direct-write method. Electron-beam-induced deposition with a scanning electron microscope will yield locally confined deposition in the sub-50 nm range. Simultaneous introduction of up to 3 precursor gases will enable deposition of metal alloys. For synthesis of Si-NWs a dedicated LPCVD-reactor will be used. Si-NWs are synthesized by chemical vapor deposition following a catalysed vapor-liquid-solid mechanism. Project Plan Based on previous own research this work will address new challenges in 2 disciplines: Fabrication of metal alloy templates on prestructured 3D substrates Electron beam induced deposition (EBID) is used to fabricate metal alloy nanoparticles by maskless direct- writing. Predefined patterns of metal alloy nanoparticles on planar and 3-dimensionally prestructured substrates will be fabricated as catalytic template for nanowire synthesis. Synthesis of epitaxial silicon nanowires on predefined positions using catalytic nanoparticle templates The beam-tailored catalyst templates enable new opportunities in nanowire synthesis. On predefined positions epitaxial Si-nanowires will be grown by CVD from inorganic silicon precursors. The new approach enables synthesis of Si-nanowires on 3-dimensional prestructured substrates with arbitrarily oriented crystalline surfaces. The catalytic properties of various metals and alloys will be investigated. Relevance The unique combination of contemporary methods will break new ground scientifically by (i) the first EBID deposition of alloys and (ii) the accurate positioning of nanowires on non-flat surfaces. The EBID-deposition of alloys with controlled composition will enable to tailor catalysts with a suitable melting point enabling NW growth at moderate temperatures. The nanoparticle deposition on 3-dimensionally prestructured substrates will stimulate Si-NW growth on custom-designed templates. For the first time the positioning of NWs on specific locations of 3- dimensional substrates becomes possible. This enabling technique significantly improves the application potential of Si-NWs for functional device structures such as 1-dimensional electronic devices (nanowire transistor), sensitive biosensors and field emitter devices.