Ferroelectricity in sub-10 nm thick 3D hafnium zirconium oxide layers

In this work, the ferroelectric behavior of three-dimensional Hafnium Zirconium Oxide (HZO) capacitors is investigated. Integrated metal ferroelectric metal capacitors with HZO layers of thicknesses ranging from 6 to 10 nm were fabricated using atomic layer and chemical vapor deposition techniques. The influence of the main geometric and thermal parameters, including aspect ratio, HZO thickness, and rapid thermal annealing temperature, is evaluated through structural and electrical characterization. The crystallographic structure of the devices is characterized using fixed incidence angle x-ray diffraction. Improved crystallinity and increased peak intensity are observed with increasing annealing temperature and HZO thickness. In addition, samples with a higher aspect ratio show higher peak intensities compared to samples with a lower aspect ratio. The structural analysis shows the formation of the HZO orthorhombic phase at annealing temperatures as low as 380 °C for 10 nm thick films. For electrical characterization, the Positive Up Negative Down technique is employed to determine remanent polarization (2Pr) from the hysteresis loops of ferroelectric capacitors. Higher aspect ratio samples recorded higher values of 2Pr, which also improves with both thicker HZO films and higher annealing temperatures. Endurance testing revealed that films annealed at 450 °C exhibited electrical stability, preserving endurance beyond 106 switching cycles before breakdown. These results highlight the significance of 3D structural design and the role of aspect ratio in enhancing ferroelectric behavior in scaled memory devices. The results also emphasize the need to carefully optimize both the thermal treatment and film thickness to achieve stable and high-performance ferroelectric capacitors.