Suppression of interfacial layers in ZrO2/TiN capacitors by atomic layer deposition using ligand-engineered Zr precursors for scalable DRAM

Abstract

As dynamic random-access memory continues to scale down, the feasible physical thickness of the capacitor dielectric layer continuously decreases, thus, controlling the low-k interfacial layer formed at the ZrO₂ dielectric/TiN electrode interface is becoming crucial. The interfacial layer reduces the capacitance density and increases the leakage current density, and both of them contribute to the degradation of the overall properties of the capacitor. In this study, two precursors were compared: the commonly used Cp-based Zr precursor, Cp–Zr(NMe₂)₃ [Cp–Zr] and the novel MePrCp–Zr(NMe₂)₃ [MePrCp–Zr] precursor, with the two terminal hydrogens of the Cp ligand substituted with Me and Pr groups. MePrCp–Zr was confirmed to suppress the formation of low-k interfacial layers such as TiO_x or TiO_xN_y at the initial ZrO₂ growth stage, owing to its higher reactivity than Cp–Zr. Furthermore, analysis of oxidation behavior using TiN and Ru bottom electrodes clearly revealed that the application of MePrCp–Zr led to improved interfacial sharpness compared to Cp–Zr. Electrical properties also confirmed enhanced interfacial properties, indicating that the equivalent oxide thickness decreased by 0.38 nm with the MePrCp–Zr precursor compared to Cp–Zr. This ligand-engineering strategy provides a scalable approach to achieving ultrathin high-k dielectrics with stable interfaces, enabling reliable capacitor integration for next-generation DRAM and advanced logic technologies.