Interface Properties of Pr_xAl_2-xO₃ (x = 0 to 2) Dielectrics on TiN Studied by Synchrotron Radiation X-ray Photoelectron Spectroscopy

Abstract

Extending the scalability of deep trench capacitor dynamic random access memories requires introduction of a high-k dielectric-based storage capacitor structure. Pr-enriched Al₂O₃ dielectrics with TiN electrodes appear as a promising materials system for this application. Electrical measurements performed on this materials combination show, however, that achieving a very low capacitance equivalent thickness and low leakage current requires very careful control of the electrode/dielectric interface properties. In particular, formation of a parasitic interface layer has to be avoided. For this purpose, we carried out a systematic synchrotron radiation x-ray photoelectron spectroscopy study to non-destructively investigate the interface reactivity of the Pr_xAl_2-xO₃ (x = 0, 1, 2)dielectrics with TiN metal electrodes. The depth profiling study shows that the TiN substrate is covered with a native TiO₂. Additionally, a thin interfacial Ti oxynitride layer is present between these compounds, resulting in a TiN/TiNO/TiO₂ materials stack. Molecular beam deposition of Al₂O₃ onto substrates of this structure leads to a remarkable reduction of the native oxide. In contrast, in the same way deposited PrAlO₃ and Pr₂O₃ dielectrics are significantly less reactive towards TiO₂. As a consequence, the native TiON/TiO₂ remains the main component of the interface layer in the TiN/PrAlO₃ and TiN/Pr₂O₃ capacitor stacks. Such a configuration poses severe scalability problems to the Pr aluminate dielectrics.