The surface chemistry of the bis(tri-n-butylphosphane) copper(I) acetylacetonate, [( n Bu 3 P) 2 Cu(acac)] and the thermal atomic layer deposition (ALD) of Cu 2 O using this Cu precursor as reactant and wet oxygen as coreactant on SiO 2 substrates are studied by in-situ x-ray photoelectron spectroscopy (XPS). The Cu precursor was evaporated and exposed to the substrates kept at temperatures between 22 C and 300 C. The measured phosphorus and carbon concentration on the substrates indicated that most of the [ n Bu 3 P] ligands were released either in the gas phase or during adsorption. No disproportionation was observed for the Cu precursor in the temperature range between 22 C and 145 C. However, disproportionation of the Cu precursor was observed at 200 C, since C/Cu concentration ratio decreased and substantial amounts of metallic Cu were present on the substrate. The amount of metallic Cu increased, when the substrate was kept at 300 C, indicating stronger disproportionation of the Cu precursor. Hence, the upper limit for the ALD of Cu 2 O from this precursor lies in the temperature range between 145 C and 200 C, as the precursor must not alter its chemical and physical state after chemisorption on the substrate. Five hundred ALD cycles with the probed Cu precursor and wet O 2 as coreactant were carried out on SiO 2 at 145 C. After ALD, in-situ XPS analysis confirmed the presence of Cu 2 O on the substrate. Ex-situ spectroscopic ellipsometry indicated an average film thickness of 2.5 nm of Cu 2 O deposited with a growth per cycle of 0.05 Å /cycle. Scanning electron microscopy and atomic force microscopy (AFM) investigations depicted a homogeneous, fine, and granular morphology of the Cu 2 O ALD film on SiO 2 . AFM investigations suggest that the deposited Cu 2 O film is continuous on the SiO 2 substrate.

The growth of ultrathin (<5 nm) Ru-doped Cu 2O films deposited on SiO2 by atomic layer deposition (ALD) and Cu films by subsequent reduction of the Cu 2O using HCO2H or CO is reported. Ru-doped Cu 2O has been deposited by a mixture of 16: 99 mol. % of [( n Bu3P)2Cu(acac)] as Cu precursor and 17: 1 mol. % of [Ru(η 5-C7H11)(η 5-C5H4SiMe3)] as Ru precursor. The catalytic amount of Ru precursor was to support low temperature reduction of Cu 2O to metallic Cu by formic acid (HCO2H) on arbitrary substrate. In situ x-ray photoelectron spectroscopy investigations of the Cu 2O ALD film indicated nearly 1 at. % of carbon contamination and a phosphorous contamination below the detection limit after sputter cleaning. Systematic investigations of the reduction of Ru-doped Cu 2O to metallic Cu by HCO2H or CO as reducing agents are described. Following the ALD of 3.0 nm Cu 2O, the ultrathin films are reduced between 100 and 160 °C. The use of HCO2H at 110 °C enabled the reduction of around 90% Cu 2O. HCO2H is found to be very effective in the removal of oxygen from Ru-doped Cu 2O films with 2.5–4.7 nm thickness. In contrast, CO was effective for the removal of oxygen from the Cu 2O films only below 3.0 nm at 145 °C. Root mean square surface roughness of 0.4 ± 0.1 nm was observed from atomic force microscopy (AFM) investigations after the ALD of Cu 2O, followed by the subsequent reduction of 3.0 nm Cu 2O using either HCO2H at 110 °C or CO at 145 °C on SiO2. Furthermore, ex situ low energy ion scattering and AFM investigations confirmed that the Cu 2O film after ALD and Cu films after subsequent reduction was continuous on the SiO2 substrate

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