The Stabilization by Morphotropic Phase Boundary with a MoO_x Cap on Hf_1−xZr_xO₂ Dielectrics

Hf_1−xZr_xO₂ (HZO) high-k dielectrics were fabricated by plasma-enhanced atomic layer deposition (PE-ALD). A conformal MoO_x cap with high-thermal stability was then deposited before high-temperature post-metal annealing. Diffraction peaks of HZOs corresponding to orthorhombic (o)- and tetragonal (t)-phases are located at 2θ = 30.0–30.5°, where the angle of o-phase is slightly lower than that of t-phase. The increase in intensity of o-phase results in high ferroelectricity, which is consistent with polarization-electric field (P-E) characteristics. The relative dielectric constant (k) close to 35 is detected in a wide Hf/Zr cycle ratio ranging from 3 to 1/3, despite dielectric enhancement typically being associated with the morphotropic phase boundary (MPB) at a specific o-to-t phase ratio. Although the leakage currents with and without the MoO_x cap are comparable, the temperature-dependent current conduction mechanisms differ. The predominance of Schottky emission after capping suggests the formation of a high-quality interface. These findings demonstrate that surface passivation with an ultra-thin MoO_x layer is an effective approach for maximizing the dielectric constant of HZO across a wide compositional window.