Unlocking the Potential of Hafnia Ferroelectrics: Achieving High Reliability via Plasma Frequency Modulation in Very High-Frequency Plasma-Enhanced Atomic Layer Deposition

Abstract

Hafnia ferroelectrics are gaining significance in nonvolatile memory, logic devices, and neuromorphic computing because of their rapid switching speed, exceptional reliability, and low-voltage operations. In addition, it demonstrates exceptional process compatibility with advanced thin film techniques such as atomic layer deposition (ALD). Conventical radio frequency (RF) plasma-enhanced (PE) ALD offers various advantages including enhanced reaction rates, improved film characteristics, and a lower process temperature. However, the inevitable plasma damages and interfacial defects that occur as a result of the RF PE-ALD process have a major impact on the polarization hysteresis features of hafnia ferroelectrics. In our study, we fabricated a Hf_0.5 Zr_0.5O₂ (HZO) film utilizing a very high frequency (VHF) (∼100 MHz) PEALD. This approach demonstrated greater effectiveness in radical reactions and efficiently mitigated plasma-induced damage in the HZO film. The utilization of high-frequency plasma enhances stability and exhibits excellent ferroelectric characteristics. Specifically, it led to an increase in the interfacial capacitance, a decrease in the wake-up effect, and a reduction in the proportion of suboxide in HZO films. Our observations revealed exceptional switching speed (60 ns) and outstanding reliability (10¹⁰ cycles) along with a retention rate of 94% over a span of 10 years at a temperature of 85 °C. The research demonstrates that VHF PE-ALD is a viable method for creating hafnia thin films with reduced defects at the interface.