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

Abstract

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 O 2 treatment, and excessive thermal annealing is detrimental to the desired shape fidelity. Milder purification protocols based on electron irradiation in the presence of H 2 O 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) 2 Ru). 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 O 2 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.

Combined Ammonia and Electron Processing of a Carbon-Rich Ruthenium Nanomaterial Fabricated by Electron-Induced Deposition

“…Model deposits were fabricated from (EtCp) 2 Ru using a slightly modified protocol, as described in reference [9]. Briefly, precursor vapor was leaked into the UHV chamber via a gas handling manifold, where the pressure was measured with a Baratron pressure transducer with mTorr reading.…”

“…Briefly, precursor vapor was leaked into the UHV chamber via a gas handling manifold, where the pressure was measured with a Baratron pressure transducer with mTorr reading. An amount of precursor vapor corresponding to a pressure drop of 2 mTorr in the manifold was condensed onto the cooled Ta sheet, resulting in a coverage of 7-10 monolayers (ML) [9]. The film was then irradiated at E 0 = 31 eV with a total dose in the range 40-60 mC/cm 2 .…”

“…The film was then irradiated at E 0 = 31 eV with a total dose in the range 40-60 mC/cm 2 . For a dose of 40 mC/cm 2 , ESD of desorbing products had ceased according to our recent study [9]. Material retained under cryogenic conditions was subsequently desorbed by a TDS run and a bakeout (450 K for 30 s).…”

“…As a particularly successful and mild post-deposition purification process, electron irradiation in the presence of H 2 O vapor was recently brought forward. This process was applied to deposits produced from the precursors trimethyl(methylcyclopentadienyl)-platinum(IV) (MeCpPtMe 3 ) [6], tetrakis(trifluorophosphine)platinum(0) (Pt(PF 3 ) 4 ) [7], dimethyl(acetylacetonate) gold(III) (Me 2 Au(acac)) [8], and, more recently, from bis(ethylcyclopentadienyl)ruthenium(II) ((EtCp) 2 Ru) [9]. In all cases, the carbon residue was efficiently removed and it was demonstrated that even the shape of complex 3D nanostructures can be preserved during such treatment [8].…”

“…While FEBID generally strives to produce highly pure metals, impure deposits may also have interesting properties. Such deposits are often nanogranular materials consisting of metal nanoparticles embedded in an amorphous carbonaceous matrix [6,9,12]. For instance, Pt in a carbonaceous matrix deposited from MeCpPtMe 3 can serve as humidity [13] or strain sensing material [14].…”