Optimization of the 4 nm-Thick Hf1–xZrxO2 Film with Low Operating Voltage and High Endurance for Ferroelectric Random Access Memory

Abstract

The integration of ferroelectric-doped HfO₂ thin films in advanced memory has been impeded by high coercive fields (E_C), requiring high operation voltages. The extremely small feature size of the state-of-the-art memory device requires film thickness <5 nm, causing electrical reliability concerns and inefficient ferroelectric orthorhombic phase formation. This research addresses these challenges by optimizing 4 nm-thick (Hf,Zr)O₂ (HZO) thin films to enable low-voltage operation with high reliability. It was noted that such an ultrathin film tends to stabilize the tetragonal phase compared to the more commonly researched 10 nm-thick HZO film due to the smaller grain size of the thinner film. Therefore, the capacitor fabrication conditions were reevaluated to destabilize the tetragonal phase while increasing the desired orthorhombic phase by decreasing the oxygen vacancy (V_O) concentration in the film. By adjusting the ozone dose time, Zr ratio, crystallization annealing temperature, and TiN capping electrode thickness, the ferroelectric properties of the 4 nm-thick film were significantly enhanced. The decreased V_O concentration also contributed to improving the capacitor reliability. The optimized 4 nm-thick HZO films exhibited outstanding ferroelectric properties, with a double coercive voltage (2 V_C) of ∼0.8 V, a double remanent polarization (2P_r) of ∼25 μC/cm² at ±1 V, and 10¹¹ endurance, satisfying gigabit density ferroelectric random access memory requirements.