Water-Assisted Process for Purification of Ruthenium Nanomaterial Fabricated by Electron Beam Induced Deposition

The purity of nanomaterials fabricated by focused electron beam induced deposition (FEBID) is often not high enough for the desired application. For instance, large amounts of carbon incorporated into the deposits deteriorate their electrical conductivity. Such impurities stem from incomplete electron-induced fragmentation of the applied precursors. Except for nanomaterials containing the most noble and thus oxidation-resistant metals, deposits cannot be purified by harsh post-processing steps like O2 treatment, and excessive thermal annealing is detrimental to the desired shape fidelity. Milder purification protocols based on electron irradiation in the presence of H2O vapor have thus been developed, and it was demonstrated that they yield pure Pt and Au deposits. Herein, we report on the application of such a water-assisted purification strategy to deposits produced from the FEBID precursor bis(ethylcyclopentadienyl)ruthenium(II) ((EtCp)2Ru). Such Ru nanomaterials are relevant to the repair of masks for extreme ultraviolet lithography. In contrast to noble metals, where higher doses lead to higher purity, and contrary to purification using O2 that is accompanied by a continuous increase of the oxygen content, we here demonstrate the existence of an ideal purification dose for Ru-based FEBID materials, where oxidation is kept at a minimum, while carbon is effectively removed from the deposits. In addition, a complementary surface study under ultrahigh vacuum conditions provides insights into the chemistry that transforms the carbonaceous contamination into CO. The results provide evidence that water-assisted purification can be applied to a wider range of FEBID deposits also including those containing Ru as an example of a less noble metal.