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 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

Two-Step Approach for Conformal Chemical Vapor-Phase Deposition of Ultra-Thin Conductive Silver Films

“…At last, we investigate the conformality of the deposition, which is one of the major advantages of CVD methods as compared to PVD, with the possibility of covering 3D structures with high complexity (Figure a,b). For this purpose, we have investigated the conformal synthesis of Ag thin films on 3D structures with a lateral high aspect ratio (LHAR) from PillarHall technology. ,,,, Although ALD is the most promising technique for conformal deposition, the PE-ALD of the Ag thin film suffers from the recombination of plasma species (radicals) on the surfaces, which prevents the growth deeper into such a structure. , …”

“…1,44,45,64,65 Although ALD is the most promising technique for conformal deposition, the PE-ALD of the Ag thin film suffers from the recombination of plasma species (radicals) on the surfaces, which prevents the growth deeper into such a structure. 2,35 We demonstrate in Figure 6c−e that we managed to produce Ag thin layers extremely conformal on top, bottom, and at the back of an LHAR with an aspect ratio of 100. As compared to this result, the standard PE-ALD method gives poor uniformity over LHAR trenches with no deposition on the back (Figure S2, Supporting Information).…”

“…A two-step approach consisting of the deposition of a metal-containing film subsequently reduced to a metallic state was proved for copper thin layers. 2,35 However, this will be difficult to transfer to silver coatings as stable Ag (II) complexes are extremely complex to obtain, mainly due to their more noble character as compared to Cu. At last, Al and Cu doping has demonstrated strong reduction of the Ag film roughness and critical thickness of films deposited by sputtering, 14−16 although a similar attempt has not yet been reported for ALD or CVD.…”

Atomic Layer Deposition of Superconducting CuO Thin Films on Three-Dimensional Substrates

“…Cu 2 O possesses moderate electron mobility, and the Cu 2 O films, epitaxially grown on MgO by pulsed laser deposition, were examined as thin film transistor channels [5]. The formation of interconnecting Cu bias between transistors in a computing processor can be made by the initial growth of Ru-doped Cu 2 O films, followed by their reduction to Cu [6]. Cu 2 O films were studied also as photoconductive materials [7,8].…”