Ferroelectric Hf0.5Zr0.5O2 (HZO) thin films emerge as promising candidates for next-generation memory devices; however, the device performance is strongly correlated to the interfacial structure. In this study, neutron reflectivity was used for the first time to conduct an in-depth analysis of the ferroelectric W/HZO/W devices, leveraging the high sensitivity of neutron scattering length density (SLD) to the buried interfaces. We explored the impact of different atomic layer deposition (ALD) techniques─thermal, plasma, and atomic layer annealing (ALA)─on the structural and ferroelectric characteristics of HZO thin films, with a particular focus on interfacial structures. Analyses using neutron reflectivity, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy revealed the critical role of the bottom WOx interfacial layer. The ALA treatment contributes to significant enhancements in structural and ferroelectric properties, including an increase in film density and crystallinity, as well as a maximum neutron SLD due to reduced oxygen vacancies. This work elucidates the crucial role of interface engineering via interfacial layer formation in stabilizing the ferroelectric phase, providing valuable insights for the development of advanced ferroelectric devices.

In this study, platinum (Pt) and tungsten (W), two materials with dissimilar coefficients of thermal expansion (CTE) and work functions (WF), are used as the top electrode (TE) and the bottom electrode (BE) in metal/ferroelectric/metal (MFM) structures to explore the ferroelectricity of hafnium zirconium oxide (HZO) with a thickness less than 10 nm. The electrical measurements indicate that a higher CTE mismatch between HZO and TE/BE is beneficial for enhancing the ferroelectric properties of nanoscale HZO thin films. The different WFs of TE and BE generate a built-in electric field in the HZO layer, leading to shifts in the hysteresis loops and the capacitance-voltage characteristics. The structural characterizations reveal that the preferred formation of the orthorhombic phase in HZO is dominated by the W BE. The device in which W is used as the TE and BE (the W/HZO/W MFM structure) presents the optimal ferroelectric performance of a high remanent polarization (2Pr= 55.2μC cm-2). The presence of tungsten oxide (WOx) at the W/HZO interfaces, as revealed by high-resolution transmission microscopy, is also responsible for the enhancement of ferroelectric properties. This study demonstrates the significant effects of different CTEs and WFs of TE and BE on the properties of ferroelectric HZO thin films.

A high-quality nanoscale oxide layer with a high dielectric constant and a low leakage current prepared at a low thermal budget is critical to advanced metal-insulator-metal (MIM) devices. In this study, the film density, crystallinity, dielectric constant, and leakage current of the ZrO2 thin film are significantly improved by the atomic layer annealing (ALA) and the titanium nitride (TiN) capping layer effect at a low process temperature of only 300 degrees C without any postannealing treatment. Hence a high ZrO2 dielectric constant of 35.2, a low equivalent oxide thickness of 0.64 nm, and a leakage current density lower than 10-7 A/cm2 are demonstrated in the MIM capacitors. This study demonstrates the significant impacts of the ALA and capping layer effects on the film quality and electrical characteristics of nanoscale thin films for high-performance devices.

In the recent decade, there is a growing interest in Hf0.5Zr0.5O2 (HZO) thin films owing to their well-behaved ferroelectricity and high compatibility with semi-conductor integrated circuit technology. The ferroelectric properties of HZO are highly pertinent to the wake-up effect, which has been reported to be associated with the monoclinic (m-), orthorhombic (o-), and tetragonal (t-) phases. However, it is very challenging to distinguish the o-and t-phases by conventional X-ray diffraction. In this study, the HZO thin films with and without the need for the wake-up process to enhance the ferroelectricity were prepared, and the precession electron diffraction (PED) phase mapping technique was utilized to identify the crystalline phases in the HZO layers. The PED characterization reveals the correlation between the phase transformation and the wake-up effect in HZO. The absence of the t-phase is responsible for the wake-up-free property in the ferroelectric HZO thin film. The wake-up-free and pronounced ferroelectricity of the nanoscale HZO thin film in this study may bring a practical impact on a variety of ferroelectric applications.

Tailoring the work function of metal gates at a low temperature is critical to the electronic performance of advanced nanoscale MOSFET devices. In this paper, the work function of TiN thin films is effectively altered by the atomic layer annealing (ALA) technique, i.e. the layer-by-layer, in-situ argon plasma treatment incorporated into each atomic layer deposition cycle. The density, stoichiometry, and crystallinity of TiN thin films can be significantly improved by the ALA treatment at a low temperature of only 300 degrees C, which leads to a wide tunability of the work function from 4.52 to 4.03 eV of the TiN metal gate. The sufficiently low work function of 4.03 eV is highly favorable to the low power consumption in n-type MOSFETs. The result indicates that the ALA technique is an advantageous approach to modulating the physical and material properties of metal gates in nanoscale MOS devices by precise energy transfer with atomic-scale accuracy.

Attentions on HfO2-based ferroelectric thin films have been rapidly raised due to the promising non-volatile memory applications in advanced artificial intelligence. In this study, the novel "atomic layer substrate bias induced crystallization (ALCISB)" technique is proposed to prepare wake-up free and back-end-of-line compatible Hf0.5Zr0.5O2 (HZO) thin films. The adatom migration boosted by the energy transfer from the plasma in the ALCISB process contributes to the film densification and the crystallinity enhancement of the HZO layer. The ferroelectric remnant polarization (2Pr) and the dielectric constant are increased from 3 to 48 μC/cm2 and 21.4 to 27.7, respectively, which are attributed to the crystallization into orthorhombic phase by the ALCISB technique. Furthermore, the ALCISB treatment suppresses the amount of oxygen vacancies, leading to the extension of the endurance up to 109 cycles and the wake-up free operation of the HZO thin film. The retention characteristic is almost free of degradation after extrapolating to 10 years of thermal treatment. The exceptional ferroelectric properties of the HZO thin films synthesized by ALCISB are highly favorable to non-volatile ferroelectric memory devices in the near future.