Development of vacuum ultraviolet multichannel ellipsometry and its application to the characterization of ultrathin zirconium oxide films

Abstract

Vacuum ultraviolet spectroscopic ellipsometry (VUV SE) was developed with a multichannel detection system. This system can cover up to 8.5 eV with brief nitrogen purge through optical path. We applied this technique to the characterization of zirconium oxide (ZrO(2))films for which the conventional spectroscopic ellipsometer fails due to the poor sensitivity. ZrO(2) is one of the high-k dielectrics which can be used for the storage capacitor in dynamic random access memory devices. However, due to the large leakage current of ZrO(2), thin layer of aluminum oxide (Al(2)O(3)) is sandwiched between two ZrO(2) layers forming 'ZrO(2)(top)/Al(2)O(3)/ZrO(2)(bottom)'. This structure also prevents the reaction between Al(2)O(3) and electrodes during deposition. As overall thickness of this structure is less than 10 nm, the thickness and the properties of each layer need to be controlled precisely in order to fabricate a well-defined capacitor. However, the optical properties of ZrO(2) films are highly dependent on the preparation process and conditions. Thus, many considerations are required for the analysis of VUV SE data. Through the complicated analysis, we found that the optical properties of the bottom ZrO(2) film are dependent on its own thickness as well as the deposition temperature for the subsequent Al(2)O(3) layer. Moreover, those of the top ZrO(2) layer showed the dependence on the crystalline structure of the bottom ZrO(2) along with the thickness of interfacial Al(2)O(3) layer.