Interface formation during the yttrium oxide deposition on Si by pulsed liquid-injection plasma enhanced metal-organic chemical vapor deposition

Abstract

In this article, we investigate the main mechanisms of interfacial SiO2 and silicate formation during yttrium oxide deposition on Si substrates by plasma-enhanced metal-organic chemical vapor deposition using a pulsed-liquid injection delivery source. The precursor supplier system is based on a sequential injection of Y-precursor diluted in an organic solvent. A detailed study of interface thickness and chemical nature is carried out combining angle-resolved x-ray photoelectron spectroscopy, transmission electron microscopy, and electron energy loss spectroscopy. We found that the flow rate of injected reactive species, controlled by the injection frequency, has a strong effect on the plasma gas phase and plays a key role in the SiO2 and silicate formation. For a 1Hz injection frequency deposition, a silicate layer is formed on a thick SiO2 interface [Si∕SiO2(∼3.6nm)∕SixOyYz], whereas deposition at 5Hz induces an oxidized yttrium layer with an interfacial layer composed of a SiO2 and Y-silicate mixture [Si∕SiO2+SixOyYz(∼2nm)∕YxOyCz]. To understand the actual SiO2 origin, the effect of the oxygen plasma on the silicon oxidation was investigated. According to our results, the silicon oxidation by the oxygen O* species from the plasma is strongly enhanced by the presence of organic compounds in the plasma gas phase from reactions between the solvent molecule and the oxygen. This reaction is mostly favored at a low solvent flow rate, which can explain the thicker SiO2 layer observed for the 1Hz sample compared to the 5Hz. When introducing yttrium precursor in addition to the solvent, a Y-based silicate is formed via consumption of the SiO2 by yttrium. The silicate formation is enhanced when a large quantity of SiO2 is available, which is the case for the 1Hz sample. According to this study, a high flow of reactive species is preferred to reduce the interface layer thickness.