Comparative study of Cu precursors for 3D focused electron beam induced deposition

The copper precursors bis-hexafluoroacetylacetonato-copper Cu(hfac)2, vinyl-trimethyl-silane-copper(I)-hexafluoroacetylacetonate (hfac)Cu(VTMS), 2-methyl-l-hexen-3-yne-copper-hexafluoroacetylacetonate (hfac)Cu(MHY), and dimethylbutene-copper(I)-hexafluoroacetylacetonate (hfac)Cu(DMB) are compared with respect to deposition rates and metal content obtained by focused electron beam induced deposition. Exposure was performed with 25 keV electrons in a Cambridge S100 scanning electron microscope equipped with a lithography system. Tip deposition rates increase with increasing precursor vapor pressure and range between 47 nm/s for (hfac)Cu(DMB) to about 4 nm/s for Cu(hfac)2. A decay of deposition rates with time, i.e., tip length, is observed. Electric 4-point measurements indicate an insulating behavior of deposited lines for all precursors. In contrast, Cu contents of up to 45-60 atom % were found by Auger electron spectroscopy in thin rectangular deposits using (hfac)Cu(DMB) and (hfac)Cu(VTMS) as precursors. A discussion in terms of monolayer coverage, completeness of precursor molecule dissociation, and precursor stability is presented.