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

The surface chemistry of the bis(tri-n-butylphosphane) copper(I) acetylacetonate,[((Bu3P)-Bu-n)(2)Cu(acac)] and the thermal atomic layer deposition (ALD) of Cu2O using this Cu precursor as reactant and wet oxygen as coreactant on SiO2 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 degrees C and 300 degrees C. The measured phosphorus and carbon concentration on the substrates indicated that most of the [(Bu3P)-Bu-n] 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 degrees C and 145 degrees C. However, disproportionation of the Cu precursor was observed at 200 degrees 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 degrees C, indicating stronger disproportionation of the Cu precursor. Hence, the upper limit for the ALD of Cu2O from this precursor lies in the temperature range between 145 degrees C and 200 degrees 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 SiO2 at 145 degrees C. After ALD, in-situ XPS analysis confirmed the presence of Cu2O on the substrate. Ex-situ spectroscopic ellipsometry indicated an average film thickness of 2.5 nm of Cu2O deposited with a growth per cycle of 0.05 angstrom/cycle. Scanning electron microscopy and atomic force microscopy (AFM) investigations depicted a homogeneous, fine, and granular morphology of the Cu2O ALD film on SiO2. AFM investigations suggest that the deposited Cu2O film is continuous on the SiO2 substrate