Uniform Crystal Formation and Electrical Variability Reduction in Hafnium-Oxide-Based Ferroelectric Memory by Thermal Engineering

Abstract

In this paper, we achieved excellent variation control, endurance enhancement, and leakage reduction in zirconium (Zr)-doped hafnium oxide (Hf 1−x Zr x O 2 ) based ferroelectric films by the germination of large ferroelectric grains through extending the duration of rapid thermal annealing without increasing the temperature beyond 700 °C. The pivotal point of this work is to reduce electrical variations in ferroelectric capacitors, which we attribute to the random variation in ferroelectric and dielectric phases. The motivation for this research originally stemmed from Johnson− Mehl−Avrami−Kolmogorov's theory of nucleation, which predicts that a sufficient time is required for forming any particular phase during phase transformation. Instead of increasing the temperature beyond 700 °C, extending the duration of rapid thermal annealing allows uniform crystal to form, which agrees with the theory. A 10 nm thick Hf 1−x Zr x O 2 film (x = 0.2) has been fabricated. The duration and temperature of rapid thermal annealing (RTA) under a nitrogen (N 2 ) atmosphere at 1 atmospheric pressure (atm) is varied to observe its effect on crystal formation and the electrical properties of the devices. It was observed that very low temperature and short (30 s) duration annealing at 1 atm pressure cannot infuse ferroelectricity in Hf 1−x Zr x O 2 . Structural analysis clearly showed the formation of large and uniform ferroelectric domains with negligible impact on surface roughness upon extending the annealing duration up to 180 s. The device-to-device variation in terms of standard deviation of coercive voltage and peak capacitance are reduced from 400 to 17 mV and from 20 to 4 fF/cm 2 , respectively, by increasing the RTA duration at 700 °C. The devices have also displayed endurance above 1 million cycles and leakage current density below 10 pA/μm 2 . The simple physics-based process discussed here reduces the thermal budget required for Hf 1−x Zr x O 2 , mitigates the randomness in the domain distribution, and infuses deterministic switching. This improvement paves the way for implementing Hf 1−x Zr x O 2 -based, deeply scaled ferroelectric devices for memory and steep slope device applications.

Random and Systematic Variation in Nanoscale Hf0.5Zr0.5O2 Ferroelectric FinFETs: Physical Origin and Neuromorphic Circuit Implications

“…Nanoscale n-type and p-type tri-gate Fe-finFETs were fabricated on an SOI wafer using a gate first self-aligned high-K and metal gate process (De et al, 2021b). The devices under consideration have a gate length (L) of 70 nm and fin width (W) of 20 nm.…”

“…The second is parasitic charge clouds at the interface and fin line-edge-roughness (LER), which increases the charge-trapping probability and inhibits fast WRITE. Previous reports have shown that surface treatment can alleviate the issues associated with the poor interface quality and reduce the device-to-device variations up to a maximum 10% deviation from the mean value (De et al, 2021a;De et al, 2021b). The final and third one is systematic retention degradation, which directly impacts the inference operation (Baig et al, 2021).…”

“…The advantage of HZO over other perovskite ferroelectric materials and Sidoped hafnium oxides (HSO) has been mentioned in previous reports, which involves ease of deposition by the ALD process, scalability to thin film, and lower process temperature (Muller et al, 2012;Jerry et al, 2017;Kim H. et al, 2018;Ali et al, 2019;Ni et al, 2019;Cheema et al, 2020). Recent reports have also shown that low process temperature, superior interface quality, and reducing the numbers of defect sites in HZO improve the endurance of the HZO-based transistors (Dutta et al, 2020;De et al, 2021a;De et al, 2021b;Khakimov et al, 2021). Apart from the device structure, low process temperature and interface properties, the pulse scheme, and bias-technique during the WRITE operation also play an important role in determining the WRITE-endurance limit of the device.…”

“…Fe-finFETs may also be used for online training, which requires constant updating of weight coefficient (memory write) during training. With endurance up to 10 9 demonstrated for HZO films (Chung et al, 2018;De et al, 2021b), such application is possible. For inference-only applications, Fe-finFETs form a memory array to perform multiply-and-accumulate (MAC) tasks.…”

Semiconducting phase of hafnium dioxide under high pressure: a theoretical studied by quasi-particle GW calculations

“…Hafnium oxide HfO 2 is a remarkable material with various applications. Currently, the Hafnium oxide-based material is mainly used as the ideal memory material, [1,2,3,4,5] i.e. ferroelectric Si-doped HfO 2 [6,7,8,9] due to its ferroelectric property.…”