Enhanced Oxidation Resistance and Interface Stability of Atomic-Layer-Deposited MoNx Electrodes via TiN Passivation for DRAM Cell Capacitor Applications

The continuous miniaturization of dynamic random-access memory (DRAM) capacitors has amplified the demand for electrode materials featuring specific characteristics, such as low resistivity, high work function, chemical stability, excellent interface quality with high-k dielectrics, and superior mechanical properties. In this study, molybdenum nitride (MoN_x) films were deposited using a plasma-enhanced atomic layer deposition (PEALD) employing bis(isopropylcyclopentadienyl)molybdenum(IV) dihydride and NH₃ plasma for DRAM capacitor electrode applications. Depending on the deposition temperatures of the PEALD MoN_x films ranging from 200 to 400 °C, the Mo/N ratio and crystal structure varied, transitioning from the cubic NaCl-B1-type MoN phase with Mo/N ratio of 1.4 to the cubic γ-Mo₂N phase with Mo/N ratio of 1.9. Notably, MoN_x films grown at 400 °C exhibited low resistivity (435 μΩ·cm), a high work function (5.28 eV), and superior mechanical hardness (11.3 GPa) compared to ALD TiN films. Despite these excellent properties, the PEALD MoN_x electrode demonstrated insufficient chemical stability, particularly in terms of oxidation resistance and interface quality with ALD Hf_xZr_1-xO₂ (HZO) films. This resulted in poor morphology and the formation of significant oxygen-deficient HZO layers (such as HfO_2-x), leading to considerable degradation in the electrical performance of metal-insulator-metal (MIM) capacitors. To mitigate this issue, a thin (2.5-14 nm) ALD TiN layer was introduced as a passivation layer between the MoN_x bottom electrode and HZO dielectric. The TiN-passivated MoN_x (TiN/MoN_x) electrode showed substantially enhanced oxidation resistance and reduced interfacial reactions with the HZO dielectric. Consequently, MIM capacitors with TiN/MoN_x bottom electrodes demonstrated outstanding electrical performance, including excellent dielectric properties, low leakage current density, and high mechanical strength. Hence, this study proposes a promising candidates for storage nodes in the next-generation DRAM capacitors.