Understanding the mechanisms of interfacial reactions during TiO_2 layer growth on RuO_2 by atomic layer deposition with O_2 plasma or H_2O as oxygen source

摘要

In this paper, TiO_2 layers grown on RuO_2 by atomic layer deposition (ALD) using tetrakis (dimethyla-mino) titanium (TDMAT) and either oxygen plasma or H_2O as oxygen source were analyzed using X-ray diffraction (XRD), Raman spectroscopy, and depth-resolved X-ray Photoelectron spectroscopy (XPS). The main objective is to investigate the surface chemical reactions mechanisms and their influence on the TiO_2 film properties. The experimental results using XRD show that ALD deposition using H_2O leads to anatase TiO_2 whereas a rutile TiO_2 is obtained when oxygen-plasma is used as oxygen source. Depth-resolved XPS analysis allows to determine the reaction mechanisms at the RuO_2 substrate surface after growth of thin TiO_2 layers. Indeed, the XPS analysis shows that when H_2O assisted ALD process is used, intermediate Ti_2O_3 layer is obtained and RuO_2 is reduced into Ru as evidenced by high resolution transmission electron microscopy. In this case, there is no possibility to re-oxidize the Ru surface into RuO_2 due to the weak oxidation character of H_2O and an anatase TiO_2 layer is therefore grown on Ti_2O_3. In contrast, when oxygen plasma is used in the ALD process, its strong oxidation character leads to the re-oxidation of the partially reduced RuO_2 following the first Ti deposition step. Consequently, the RuO_2 surface is regenerated, allowing the growth of rutile TiO_2. A surface chemical reaction scheme is proposed that well accounts for the observed experimental results.