Investigation of Laminated High-k Oxides by Using Vacuum Ultraviolet Spectroscopic Ellipsometry

Abstract

Zirconium oxide (ZrO 2 ) 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 ZrO 2 and Al 2 O 3 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 `ZrO 2 /Al 2 O 3 /ZrO 2 ' on a silicon substrate, where the oxide layers were prepared by using an atomic layer deposition technique. As the optical properties of the ZrO 2 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 ZrO 2 film depended on its own thickness, as well as on the deposition temperature of the subsequent Al 2 O 3 layer. Meanwhile, those of the top ZrO 2 layer showed a dependence on the crystalline structure of the bottom ZrO 2 and on the thickness of the interfacial Al 2 O 3 layer.