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

The purity of nanomaterials fabricated by focused electron beam induceddeposition (FEBID) is often not high enough for the desired application. For instance,large amounts of carbon incorporated into the deposits deteriorate their electricalconductivity. Such impurities stem from incomplete electron-induced fragmentation of theapplied precursors. Except for nanomaterials containing the most noble and thusoxidation-resistant metals, deposits cannot be purified by harsh post-processing steps likeO2 treatment, and excessive thermal annealing is detrimental to the desired shape fidelity.Milder purification protocols based on electron irradiation in the presence of H2O vaporhave thus been developed, and it was demonstrated that they yield pure Pt and Audeposits. Herein, we report on the application of such a water-assisted purification strategy to deposits produced from the FEBIDprecursor bis(ethylcyclopentadienyl)ruthenium(II) ((EtCp)2Ru). Such Ru nanomaterials are relevant to the repair of masks forextreme ultraviolet lithography. In contrast to noble metals, where higher doses lead to higher purity, and contrary to purificationusing O2 that is accompanied by a continuous increase of the oxygen content, we here demonstrate the existence of an idealpurification dose for Ru-based FEBID materials, where oxidation is kept at a minimum, while carbon is effectively removed from thedeposits. In addition, a complementary surface study under ultrahigh vacuum conditions provides insights into the chemistry thattransforms the carbonaceous contamination into CO. The results provide evidence that water-assisted purification