Electron Beam Lithography with Carboxylate-Modified TiO₂ Nanoparticles for Sub-20 nm Features

The integration of functional metal-oxide nanomaterials into high-performance devices is contingent on their precise patterning into two- or 3D nanostructures. Nevertheless, the limited solubility and poor film-forming properties of these materials pose significant challenges for nanopatterning. Conventional methodologies are predicated on the utilization of photoresist for the lithographic pattern transfer to metal-containing layers, a process that complicates the overall process. In this work, we present a photoresist-free lithographic approach that uses solution-processable, carboxylic acid-modified titanium oxide nanoparticles (TiO₂ NPs), which are rationally synthesized via controlled coordination-hydrolysis reactions, to realize TiO₂ nanopatterning. Electron beam exposure has been demonstrated to enable sub-20 nm patterning, achieving feature sizes as small as 14 nm without the need for an additional sacrificial photoresist layer. The patterning mechanism, involving electron-induced dissociation of carboxylic acid ligands, has been confirmed by X-ray photoelectron spectroscopy and thermogravimetric-mass spectrometry. The post-annealing treatment has been demonstrated to preserve the structural integrity of the nanopatterns, whilst concomitantly promoting the crystallization process, resulting in the formation of anatase or anatase-rutile mixtures. This method facilitates the fabrication process whilst enabling high-resolution TiO₂ patterning, thus offering a promising route for advanced device integration.