Sub-10 nm Fully Atomic-Layer-Deposited MFM Stack with Enhanced Reliability: Record-low Ileakage and Record-high EBD in 3 nm Ferroelectric HZO

This paper presents the development of ultra-thin, fully atomic-layer-deposited (ALD) metal-ferroelectric-metal (MFM) capacitors with a record-low total thickness of 9 nm, made up of 3 nm TiN, 3 nm HZO, and 3 nm TiN. These devices exhibit exceptional ferroelectric properties and reliability, setting new benchmarks for 3 nm ferroelectric (FE) layers. The key findings include:

1. Record-Low Leakage and Breakdown Electric Field (EBD): The MFM capacitors demonstrated a leakage current density of less than (10^{-3}) A/cm² at 3 MV/cm and an extremely high EBD of over 9.5 MV/cm. These results are attributed to the thinner TiN electrodes, which improve device performance by reducing oxygen scavenging and enhancing the breakdown strength.

2. Enhanced Ferroelectric Properties: The devices also achieved a low coercive voltage (2Vc < 0.65 V) and high remnant polarization (2Pr > 18 μC/μm²) even at ultra-thin dimensions, overcoming the challenges associated with thinner HZO films. The reduction in TiN thickness from 8 nm to 3 nm played a crucial role in improving the ferroelectric properties of the HZO layer. Thinner TiN electrodes facilitated the transition from polycrystalline to amorphous TiN, which promotes the formation of the ferroelectric orthorhombic (o) phase in HZO.

3. Structural Transition of TiN Electrodes: The study revealed that as TiN thickness decreased from 8 nm to 3 nm, the TiN transitioned from a polycrystalline structure, predominantly oriented along (200), to an amorphous structure. This structural change in TiN promotes better ferroelectricity in HZO by minimizing lattice mismatch, which stabilizes the o-phase of HZO, leading to improved polarization characteristics.

4. Improved Device Reliability: The thinner TiN layers also contributed to the suppression of leakage currents and enhanced the device’s endurance. The MFM capacitors demonstrated more than (10^{11}) cycles of operation without breakdown, establishing a new benchmark for the reliability of 3 nm HZO-based devices.

5. Implications for Next-Generation Memory Technologies: The results suggest that fully ALD-deposited TiN/HZO/TiN stacks hold great promise for high-density, low-voltage, and high-endurance memory devices. The findings provide insights into scaling down the MFM stack for 3D-integrated, ultra-high-density ferroelectric memories, offering significant advantages in terms of reliability, scalability, and performance.

In conclusion, the work demonstrates that thinning TiN electrodes in MFM capacitors significantly enhances both the ferroelectric and reliability performance of ultra-thin HZO layers, pushing the boundaries of ferroelectric memory technology.