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

Abstract

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 [(nBu3P)2Cu(acac)] as Cu precursor and 17: 1 mol. % of [Ru(η5-C7H11)(η5-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 3.0 nm Cu2O, the ultrathin films are reduced between 100 and 160 °C. The use of HCO2H at 110 °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 °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 °C or CO at 145 °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.