Surface chemistry of a Cu(I) beta-diketonate precursor and the atomic layer deposition of Cu2O on SiO2 studied by x-ray photoelectron spectroscopy

Abstract

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.

Thermal Chemistry of Metal Organic Compounds Adsorbed on Oxide Surfaces

“…Another family of metal organics with bridge-bonded ligands used in chemical film deposition applications is diketonates. The most common ligands used in this case are the simplest acetylacetonate (acac) − and hexafluoroacetylacetonate (hfac) − moieties, but other diketonates with larger side chains are also known. ,− In many of the reported uses of these compounds the final target has been a metal oxide film, but some examples are also available for the growth of metallic films with these precursors, especially with late transition metals. ,− Although the studies available to date suggest that diketonates may be less reactive on surfaces than amidinates, they are still prone to fragmentation upon thermal activation.…”

Recent Developments in p‐Type Oxide Semiconductor Materials and Devices

“…Research on Cu 2 O has a long history, and the fabrication of Cu 2 O thin films or nanostructures has been widely reported by various techniques, such as PLD, magnetron sputtering, and thermal oxidation; and chemical routes, such as electrodeposition, spin coating, atomic‐layer deposition, spray coating, molecular‐beam epitaxy, microwave irradiation from a Cu precursor, chemical vapor deposition, and ink printing . A summary of the most promising studies on binary copper oxide thin films is shown in Table 2 .…”

Surface chemistry of copper metal and copper oxide atomic layer deposition from copper(ii) acetylacetonate: a combined first-principles and reactive molecular dynamics study

“…9 Previous in situ X-ray photoelectron spectroscopy (XPS) results suggest that the disproportionation of the ( n Bu 3 P) 2 Cu(acac) precursor, which deposits metallic Cu and releases gaseous Cu(acac) 2 , starts above 200 1C on SiO 2 or above 125 1C on the Co substrate. 26,27 Hence, the upper temperature limit for copper ALD using this precursor lies below these temperatures. Another important issue regarding Cu b-diketonates is the redox chemistry during the ALD.…”