Mechanisms of electron-induced reactions in focused electron beam induced deposition (FEBID)

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Electron-induced chemistry of volatile precursor molecules is central to Focused Electron Beam Induced Deposition (FEBID), a very promising direct deposition technique for nanofabrication, capable of producing free-standing 3D structures of sub-10 nm size. In FEBID volatile and often organometallic precursor molecules, initially developed for chemical vapour deposition (CVD), are decomposed on a surface by a tightly focussed electron beam. Ideally, the beam would induce complete dissociation of the precursor so that the desired material, e.g., a metal or an oxide with well-defined stochiometry, remains at the surface while the organic ligands of the molecule or fragments thereof desorb. In reality, a significant amount of ligand material often remains behind and deteriorates the properties of the deposit. Aromatic ligands such as cyclopentadienyl, for instance, are difficult to remove and yield an undesired carbon matrix. Despite their favourable volatility, such precursors are thus considered unsuitable for fabrication of pure metal deposits in FEBID. However, added process gases can significantly reduce the carbon content. This project aims at identifying the electron-induced reactions involved in this purification and will evaluate if this chemistry is efficient for a wider range of precursors. This would enable a targeted strategy for development of better FEBID precursors by using or modifying readily available volatile precursors with aromatic ligands.