Investigation of laminated high-k oxides by using vacuum ultraviolet spectroscopic ellipsometry

Abstract

Zirconium oxide (ZrO2) is suggested as a good candidate for a high-k dielectric. For the storage capacitor in a dynamic random access memory, a multi-stack of ZrO2 and Al2O3 is reported to reduce the leakage current and to secure a high capacitance. In this case, however, the thickness and the properties of each layer need to be precisely controlled in order to deposit a well-defined laminated structure. Although conventional spectroscopic ellipsometry is one of the best, techniques to characterize multilayer films, it. shows poor sensitivity to high-k materials due to its limited spectral range. Thus, in this work, vacuum ultraviolet spectroscopic ellipsometry (VUV SE) and high-resolution transmission electron microscopy were employed for the laminated structure of ZrO2/Al2O3/ZrO2' on a, silicon substrate, where the oxide layers were prepared by using ail atomic layer deposition technique. As the optical properties of the ZrO2 films were so sensitive to the preparation process, many considerations were required for the analysis of the VUV SE data. From the analysis, we found that, the optical properties of the bottom ZrO2 film depended Oil its own thickness, as well as on the deposition temperature of the subsequent Al2O3 layer. Meanwhile, those of the top ZrO2 layer showed a, dependence on the crystalline structure of the bottom ZrO2 and on the thickness of the interfacial Al2O3 layer.