Effects of Work Function and Thermal Stability of Top Electrode Materials on Electrical Properties of ZrO2-Based DRAM Capacitors

초록

The effects of work function and thermal stability of top electrode (TE) materials on the electrical properties of TE/ZrO2/TiN capacitors for dynamic random-access memory applications were investigated. TEs of Au, Ag, and Al were deposited via thermal evaporation on the atomic-layer-deposited ZrO2 dielectric layer on a TiN bottom electrode. The high work function of 5.1 eV of Au induced a very stable insulating property, while Ag and Al showed relatively higher leakage current with equivalent dielectric layer fabrication process. To evaluate the interfacial properties between the electrode and dielectric as well as the thermal stability of the electrode, post-metallization annealing (PMA) was performed in an air ambient at 400 degrees C for 30 min. Ag+ ion was diffused into the ZrO2 layer and Al was oxidized to Al2O3 at the interface for Ag and Al TEs, respectively, and severe capacitance degradation occurred. However, Au TE exhibited superior interfacial properties after PMA owing to a curing effect that promoted reducing oxygen vacancies and imperfections near the TE interface, and improved both dielectric and insulating properties.

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