Atomic layer deposition of ultrathin Cu2O and subsequent reduction to Cu studied by in situ x-ray photoelectron spectroscopy

The growth of ultrathin (<5 nm) Ru-doped Cu2O films deposited on SiO2 by atomic layer deposition (ALD) and Cu films by subsequent reduction of the Cu2O using HCO2H or CO is reported. Ru-doped Cu2O has been deposited by a mixture of 16: 99 mol. % of [((Bu3P)-Bu-n)(2)Cu(acac)] as Cu precursor and 17: 1 mol. % of [Ru(eta(5)-C7H11)(eta(5)-C5H4SiMe3)] as Ru precursor. The catalytic amount of Ru precursor was to support low temperature reduction of Cu2O to metallic Cu by formic acid (HCO2H) on arbitrary substrate. In situ x-ray photoelectron spectroscopy investigations of the Cu2O 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 Cu2O to metallic Cu by HCO2H or CO as reducing agents are described. Following the ALD of 3.0nm Cu2O, the ultrathin films are reduced between 100 and 160 degrees C. The use of HCO2H at 110 degrees C enabled the reduction of around 90% Cu2O. HCO2H is found to be very effective in the removal of oxygen from Ru-doped Cu2O films with 2.5-4.7 nm thickness. In contrast, CO was effective for the removal of oxygen from the Cu2O films only below 3.0 nm at 145 degrees C. Root mean square surface roughness of 0.4 +/- 0.1 nm was observed from atomic force microscopy (AFM) investigations after the ALD of Cu2O, followed by the subsequent reduction of 3.0 nm Cu2O using either HCO2H at 110 degrees C or CO at 145 degrees C on SiO2. Furthermore, ex situ low energy ion scattering and AFM investigations confirmed that the Cu2O film after ALD and Cu films after subsequent reduction was continuous on the SiO2 substrate. (C) 2015 American Vacuum Society.