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Effects of catalytically generated atomic hydrogen (Cat-H) treatment on electrical properties of 10 nm thick sputtered hafnium-zirconium-oxide (HZO) films have been investigated. It is demonstrated that the Cat-H treatment to the as-deposited sputtered HZO film is effective to stabilize the metastable ferroelectric orthorhombic phase after crystallization. The enhancement of ferroelectricity by the Cat-H treatment is observed for the sputtered HZO films crystalized at a reduced pressure of 100 Pa, nitrogen and air, and the enhancement is pronounced for the films crystallized in nitrogen and air ambient. In addition, it is found that the Cat-H treatment also improves the stability against re-annealing.

Carrier transport properties of ferroelectric Hf0.5Zr0.5O2 thin films have been investigated on a metal–ferroelectric–metal (MFM) capacitor in the first current flow of ferroelectric poling treatment. In the current–voltage (I–V) measurement of the MFM capacitor, a kink or discontinuity point of the derivative in the I–V characteristics appears, and after a cyclic voltage sweep this kink disappears. This phenomenon is different from the ferroelectric instabilities after application of several thousand or million voltage cycles reported as wake-up and fatigue. From the analysis using a Poole–Frenkel plot of the I–V characteristics, it is suggested that irreversible trap generation by electric field application occurs in poling treatment.

The discovery of ferroelectric HfO 2 crystal phase has brought a great impact on the electronic devices society. Since then, various challenges of memory and logic applications using this material are ongoing. These device technologies equipped on LSI are expected to realize low power consumption systems with large memory capacities and new processing architectures. In order to accomplish these products, it is important to manufacture “reliable and tough” ferroelectric HfO 2 films. In this paper, we discuss the status and the issues of ferroelectric HfO 2 films for electronic devices applications.

Ferroelectric HfO2-based thin films, which have been attracting a great deal attention because of their potential use in various applications, are known for their unique properties, such as a large time-dependent imprint and wake-up effect, which differentiate them from conventional ferroelectric materials. In this study, direct piezoelectric measurement was employed to investigate the state of polarization during the retention and wake-up process without applying an electric field. The polarization-electric field hysteresis loop of a sputtered Hf0.5Zr0.5O2 (HZO) film with a thickness of 10 nm showed a time-dependent imprint at room temperature during polarization retention, and the internal electric field that generated the imprint gradually increased from 0.05 to 0.6 MV/cm. While a space charge density of more than 1 μC/cm2 is required to form such an internal electric field, it was found that the magnitude of the direct piezoelectric response did not change at all during polarization retention. On the other hand, both the remanent polarization and direct piezoelectric response increased during the wake-up process. Based on the difference in the variation over time of these two characteristics, we concluded that the non-ferroelectric layer exists at the interface between the HZO film and TaN electrode and gradually transitions to ferroelectric phases through the electric field cycle.

We have demonstrated that sub-10 nm-thick heteroepitaxial Ge films on Si (001) having smooth surfaces can be obtained by DC magnetron sputtering. Ge films grown at 350 °C preserve the smooth surfaces with a roughness root mean square (RMS) of 0.39 nm, whereas, the Ge films grown at 500 °C show significant roughness with an island-like morphology. In samples grown at 350 °C, it is confirmed that the Ge films are grown epitaxially by cross-section transmission electron microscopy (TEM) and X-ray diffraction (XRD) rocking curve measurements. Rapid thermal annealing (RTA) at 720 °C is effective in improving the crystalline quality and the degradation in the roughness is negligible. Raman spectra and an XRD reciprocal space map reveal that the epitaxial Ge grown at 350 °C show an in-plane compressive strain and that the strain continues to remain after a 720 °C RTA.

The influence of extension doping on parasitic resistance and its variability has been investigated for FinFETs. Electrical characterization of FinFETs and crystallinity evaluation of the doped fin structure are carried out for different fin thicknesses and different donor species for ion implantation, i.e., As and P. Reducing the fin thickness and the use of donor species with a larger mass cause serious degradation in the variability and median value of the parasitic resistance. Crystallinity evaluation by transmission electron microscope reveals that significant crystal defects remain after dopant activation annealing for the cases of smaller fin thickness and the implanted dopant with a larger mass. The unrecovered defects cause serious degradation in the parasitic resistance and its variability.

This work addresses nanoscale measurements of mechanical properties of ultra-thin insulator films by a dynamic indentation atomic force microscopy (DI-AFM). The ability of the DI-AFM is discussed to clarify some challenges in quantitative evaluation of stiffness and elastic modulus of 10 nm films on Ge and S.i.

Ferroelectric-gate field-effect transistor (FE-FET) is an attractive device for both memory and logic applications. The metal-ferroelectric-metal-insulator-semiconductor (MFMIS) gate stack structure is useful to solve the issue of charge unbalance between ferroelectric and metal-insulator-semiconductor (MIS) capacitors in FE-FETs. In this study, the function of the MFMIS gate stack for the improvement of subthreshold behaviors in FE-FETs is analyzed. The results indicate that the design of capacitor-area-ratio in an MFMIS structure enhances the ferroelectric poling component relative to the paraelectric component and increases the charge boost efficiency, thereby leading to improved subthreshold swing.

Phase transformation of Hf-Zr-O films with the annealing condition is investigated. It is shown that depending on the thermal budget applied to the Hf-Zr-O films, the transformation of crystal structures progresses in the order of the tetragonal phase, the orthorhombic phase, and finally the monoclinic phase. This trend is reflected on the emergence of ferroelectricity in Hf-Zr-O films. The stabilization of the metastable orthorhombic phase before transforming into the most stable monoclinic phase is discussed based on the mechanical stress caused by the volume change between crystal cells. Its evidence is demonstrated as the change of microstructure in the crystal grains.

The orthorhombic ferroelectric phase was proposed to be a metastable state between the monoclinic and the tetragonal phases. Although manifold dopants and deposition techniques were proven to be able to cause ferroelectric properties in hafnium oxide, the root causes of the stabilization are still not well understood. In this chapter, the influence of the size and valence of the dopant was analyzed together with the influence of oxygen vacancies using the physical vapor deposition technique. This allows an extraordinary control of the film composition compared to the other deposition methods. Additionally, a new doping technique is presented using an ion implantation. It will be shown that the dopant-induced HfO2 phase transition pathway is universal and not connected to a specific dopant.

In this paper, for the first time, we clarified the multidomain dynamics of ferroelectric polarization in the Negative Capacitance Field-Effect Transistors (NCFETs) by an in-house Technology Computer-Aided Design (TCAD) module. It enables self-consistent simulations among the time-dependent Landau-Khalatnikov equation and the other equations that govern operation of FETs. Our simulation reveals that domain-wall thickness $T_{\text{dw}}$ , which reflects a correlation strength between domains predominates coherency of the NC polarization. In a strong correlation (large $T_{\text{dw}}$ ) case, a coherent NC polarization is realized at least to a degree of $T_{\text{dw}}$ . On the other hand, in a weak correlation (small $T_{\text{dw}}$ ) case, perturbation from peripherals easily leads to incoherence of polarization, where a uniform polarization is split into multiple spontaneous polarization domains. This coherency breaking found to give rise to deteriorated voltage amplification of NC. Design methodology to maintain the NC coherency is also proposed.

Ferroelectric phase transformation was compared between the Hf0.5Zr0.5O2 solid solution films and the HfO2/ZrO2 nanolaminate films, prepared by sputter deposition without heat treatment and crystallized by following cap annealing. Physical analyses showed that nanolaminate structures and their interfaces were robust even after high-temperature annealing. Ferroelectricity appeared largely in the nanolaminate films than in the solid solution film, and the best performance was attained in the nanolaminate film with the cycle thickness of monolayer oxide (0.25 nm). Long period annealing cleared that the ferroelectric phase transformation is greatly accelerated in the nanolaminate films than in the solid solution films.

Stability of ferroelectricity in hafnium–zirconium oxide (HZO) films deposited by sputtering and chemical solution deposition (CSD) has been investigated. After confirming the ferroelectricity of both sputtered HZO and CSD yttrium-doped HZO (Y-HZO) films, indium-tin-oxide (ITO) was deposited by sputtering on sputtered HZO or CSD Y-HZO layer to fabricate metal-ferroelectric-semiconductor (MFS) structure. It was found that the sputtered HZO films in the MFS structure became paraelectric after re-annealing in N2 which was confirmed by both X-ray diffraction pattern and electrical measurements. On the other hand, the CSD Y-HZO films showed ferroelectric nature even after re-annealing with a negligible monoclinic phase.

It is well known that the high-k interpoly dielectric (IPD) layer is important for further scaling down of floating gate (FG) type flash memory to improve the gate coupling ratio [1, 2]. Therefore, the high-k Al2O3 layer has already been used as a blocking layer in the charge trapping (CT) type planar and bulk FinFET flash memories [3-5]. However, the high-k Al2O3 has not been used as an IPD layer in the FG type SOI-FinFET flash memories, to our knowledge. In this work, we introduce the high-k Al2O3 into the FG type triangular-fin (TF) and rectangular-fin (RF) channel SOI-FinFET flash memories, and investigate the effects of fin shape and IPD layer material on the electrical characteristics of the fabricated FG type SOI-FinFET flash memories. In the device fabrication, we used (100) and (110) oriented SOI wafers to fabricate TF and RF channels by using the orientation dependent wet etching [6]. A 30-nm-thick n+ poly-Si layer was used as the FG material. Figure 1 shows the cross-sectional STEM images of the fabricated FG-type SOI-FinFET flash memories with different channel shapes and different IPD layers. Figure 2 shows the P/E characteristics of the fabricated 3 kinds of SOI-FinFET flash memories at the same P/E condition. It is clear that a higher P/E speed, a larger memory window and a lower-voltage operation are achieved in the TF-ONA device as compared to the TF-ONO and RF-ONA ones. This result indicates that a high-k Al2O3 layer is very useful for enhancing memory window due to the improved gate coupling, and the TF channel is very suitable for the low-voltage operation thanks to the high-k of Al2O3 and the electric field enhancement at the sharp foot edges of a TF. [1] B. Govoreanu et al., IEDM 2006, p. 479. [2] H.-T. Lue et al., IEDM 2011, p. 203. [3] C. H. Lee et al., IEDM 2003, p. 613. [4] S.-K. Sung et al., VLSI 2006, p.106. [5] B. J. Tang et al., IEDM 2011, p. 219. [6] Y. X. Liu et al., VLSI 2010, p.101. Figure 1

Since the discovery of ferroelectricity in HfO2 in 2011, extensive work begin to burst forth on HfO2-based ferroelectric materials and devices. Orthorhombic phase is responsible for ferroelectricity in HfO2, which is usually stabilized by the dopant such as Al, Zr, Si, la and Y. In particular, Zr doped HfO2 (HZO) has large Pr around 20 µC/cm2 and ferroelectricity can be obtained in a wide range of Zr composition. The orthorhombic phase is a metastable phase and Migita et al. [1] reported that the orthorhombic phase of sputtered HZO film was transferred to monoclinic phase by further annealing. In this work, robustness of ferroelectric phase against the further annealing process has been investigated using sputtered HZO and solution-derived Y-doped HZO films [2]. Sputtered HZO films were prepared by room temperature deposition followed by 600 oC, 10 min annealing in N2. Y-doped HZO films were prepared by chemical solution deposition (CSD) by annealing the samples at 800 oC for 3 min in O2.[2] Ferroelectric properties were confirmed by polarization-electric field (P-E) and capacitance-voltage (C-V) measurements for both samples before the second time annealing. Then, both samples were further annealed in 400 and 600 oC in N2 to examine the robustness of ferroelectricity. It was found that sputtered HZO films become paraelectric and that X-ray diffraction (XRD) pattern shows diffraction peak from orthorhombic phase disappeared. On the other hand, CSD HZO films shows ferroelectric nature even after second time annealing with negligible monoclinic phase. Such a significant difference in robustness is presumably due to residual carbon in the CSD films. In addition, In2O3/(Y-)HZO structures are also fabricated for oxide channel thin film transistor applications and characterized, which will be presented at the conference. [1] Shinji Migita et al, Jpn. J. Appl. Phys. 58 SBBA07, 2019. [2] Mohit et al, Jpn. J. Appl. Phys. 59 SMMB02, 2020.

HfO2 ferroelectricity is promising due to CMOS compatibility and various exceptional properties compared to conventional ferroelectricity. However, the mechanism for stabilizing the ferroelectric phase is still controversial. In this study, it is found that the redox reaction at high temperature strongly influences the phase transformation kinetics during the cooling process of Ge-doped HfO2 and alters the ferroelectric phase ratio at room temperature. The transformation to the non-ferroelectric phase becomes so fast during cooling in the oxidized sample that the transformation is unavoidable even in fast cooling and deteriorates ferroelectricity. It is further revealed that while the high-temperature redox reaction itself is reversible, the transformation to the non-ferroelectric phase during cooling is an irreversible process, which dominates ferroelectricity. These results help understand ferroelectric phase formation in doped HfO2 and elaborate the fabrication process of advanced ferroelectric devices.

We consider the method to simulate negative-capacitance field-effect transistors having a ferroelectric film as a gate insulator in the framework applicable to technology computer-aided design device simulators and propose a method with complete applicability. In the method, the behavior of the polarization in ferroelectrics is described by the Landau-Khalatnikov equation and it is solved simultaneously with the Poisson equation to obtain the distribution of the polarization and electrostatic potential. Also, the proposed method enables the device simulators to take into account a factor related to forming domain structures of the polarization.

Ion implantation technique is applied for the synthesize of ferroelectric HfO 2 films. Si ions are implanted into amorphous HfO 2 films, then crystallized by annealing. It is found that crystal structures and ferroelectric properties prepared by ion implantation are similar with those prepared by co-deposition of HfO 2 and SiO 2 . Ion implantation technique is advantageous for the control of low concentration metal composition in ultrathin films and formation of ferroelectric phase in selected area.

Ferroelectric phase formation of ZrO 2 thin films is discussed by paying attention to the film deposition process and doping into ZrO 2 , by comparing with the HfO 2 counterpart. The results are showing a considerable difference between ZrO 2 and HfO 2 in terms of the stability against thermal annealing process. It is inferred that this is likely to be originated from the activation energy difference in the structural phase transitions from tetragonal to orthorhombic and subsequent orthorhombic to monoclinic phase transitions.

Stability and instability of the negative capacitance (NC) states in metal (M) / ferroelectric (F) /M /insulator (I) /semiconductor (S) structures are rigorously studied using a newly developed transient TCAD simulation, in which time-dependent Landau-Khalatnikov (LK) equation can be considered. Our transient analysis reveals that NC becomes unstable due to formation of the inversion layer and gives rise to hysteresis in the NC-state, which cannot be simulated by the steady simulation. We propose a novel FinFET, in which the F-layer is located at the gate contact holes and exhibit a design guideline to avoid the instability of the NC-state using experimentally obtained ferroelectric parameters for (Hf, Zr)O 2 .

5-nm-Thick ferroelectric Y-doped HfO2 was intensively studied. The thickness dependence of ferroelectric properties indicates that stable ferroelectric characteristics are maintained down to 5-nm-thick by taking care of doping and capping effects. Furthermore, the cycling performance shows no wake-up behavior, no obvious degradation after 108 cycles. These results not only enable us to use ferroelectric HfO 2 for practical application, but also point out intrinsic properties in ultrathin ferroelectric HfO 2 film from materials science point of view.

Display Omitted Triangular fin channel double-gate MOSFETs were fabricated on SOTB.A high threshold voltage shift was obtained in triangular fin devices.A smaller variability was confirmed in triangular fin devices by wet etching.Uniform line edges of a triangular fin were formed by wet etching.A damage-free BOX layer was obtained by the orientation dependent wet etching. Triangular fin (Tri-Fin) channel double-gate (DG) MOSFETs were successfully fabricated on (100) SOTB wafers using orientation dependent wet etching, and their electrical characteristics were systematically compared to the rectangular fin (Rec-Fin) ones by RIE. Thanks to the wide bottom area and the suppressed line edge roughness of Tri-Fins by the wet process, a higher threshold voltage (Vt) tunability and a smaller Vt variation were obtained as compared to the Rec-Fin ones. Moreover, the wet processed Tri-Fin devices provide a damage-free BOX layer, which is useful for the fabrication of multiple Vt devices with an ultrathin BOX layer.

We evaluate the impact of tunnel junction quality on the performance of tunnel field-effect transistors (TFETs). The interface between epitaxially grown channel and source surface was used as tunnel junctions. Performing a sequential surface cleaning procedure prior to epitaxial channel growth for heavily arsenic- and boron-doped Si surfaces improved the interface quality both for p- and n-TFETs. Simultaneously, the subthreshold swing (SS) values of the TFETs improved step-by-step with interface quality.

We investigated the impact of fin length ( T fin ) on the threshold voltage ( V th ) modulation by back bias ( V b ) for independent double-gate (IDG) tunnel fin field-effect transistors (tFinFETs). It was found that V th can be tuned by V b for IDG tFinFETs regardless of T fin , which can be explained by the back-gate-effect model of IDG FinFETs. For IDG tFinFETs, the slope (back-gate-effect factor ( γ )) of V th with respect to V b increases with thinning T fin . This means that T fin thinning is effective for tuning V th by V b for IDG tFinFETs. Furthermore, it was demonstrated that this back-bias-effect is consistent with the results of device simulation using an advanced nonlocal band-to-band model.

The performance of parallel electric field tunnel field-effect transistors (TFETs), in which band-to-band tunneling (BTBT) was initiated in-line to the gate electric field was evaluated. The TFET was fabricated by inserting an epitaxially-grown parallel-plate tunnel capacitor between heavily doped source wells and gate insulators. Analysis using a distributed-element circuit model indicated there should be a limit of the drain current caused by the self-voltage-drop effect in the ultrathin channel layer.

Electrical properties of Hf-Zr-O films with several thicknesses are studied. Decent ferroelectric performances are obtained in a wide range of film thickness between 6.8 and 41 nm. A drawback in Hf-Zr-O system is that the operation electric filed for the saturated ferroelectric polarization is close to the breakdown electric field. An investigation of coercive field vs. thickness reveals that HfO2-based ferroelectrics are distinct from conventional ones.

The scaled charge trapping (CT) type silicon on insulator (SOI) FinFET flash memories with different blocking layer materials of Al2O3 and SiO2 have successfully been fabricated, and their electrical characteristics including short-channel effect (SCE) immunity, threshold voltage (Vt) variability, and the memory characteristics have been comparatively investigated. It was experimentally found that the better SCE immunity and a larger memory window are obtained by introducing a high-k Al2O3 blocking layer instead of a SiO2 blocking layer. It was also confirmed that the variability of Vt before and after one program/erase (P/E) cycle is almost independent of the blocking layer materials.

Ultrashort-channel junctionless FETs (JL-FETs) were fabricated on silicon-on-insulator substrates utilizing atomically sharp V-shaped grooves produced by anisotropic wet etching. The channel length, defined as the width of the V-groove bottom, was as short as 3 nm, and the channel thickness was between 1 and 8 nm. Excellent transistor characteristics with threshold voltages that are optimal for low-power operation were obtained for both n-FETs and p-FETs when the thickness of both the channel and gate dielectric film thickness was reduced to 1 nm. The origin of the excellent electrostatic control is discussed on the basis of fringe capacitance and quantum confinement effects in a nanometer-scale ultrathin Si layer where band-gap expansion, dielectric constant reduction, and increase in the dopant activation energy become prominent. The electrical characteristics of the ultrashort channel JL-FETs were found to be very sensitive to device parameters such as the channel thickness and dopant concentration.

Performances of negative capacitance FinFETs (NC-FinFETs) at sub 10 nm gate length are analyzed with a newly developed technology computer-aided design (TCAD) simulation. This simulation fully couples the Landau-Khalatnikov (L-K) equation with the physical equations for FinFETs in 3-D. It reveals an excellent immunity against short-channel effects in NC-FinFETs owing to NC-enhancement by the gate-to-drain coupling, for the first time. NC-FinFETs with a gate length of 10 nm are projected to operate with more than 26 times energy-efficiency of conventional FinFETs.

We improved the performance of a complementary circuit comprising Si-based tunnel field-effect transistors (TFETs) by using isoelectronic trap (IET) technology. IET technology was found to increase the ON current (I ON ) 5 times in P-TFETs and 2 times in N-TFETs. The ION enhancement improved the inverter performance. In addition, ring oscillator (RO) circuit operation with the complementary TFET inverters was experimentally demonstrated for the first time. The RO circuit with IET-TFETs exhibited a higher operation frequency than that with conventional TFETs. IET technology provides a breakthrough towards realizing complementary circuits with Si-TFETs.

This work discusses the general relationship for cation and anion doping effects on the HfO 2 para-/ferroelectric transition, which will provide us a helpful instruction for precise HfO 2 ferroelectricity design. In addition, ferroelectric N-doped HfO 2 has been demonstrated as a gate dielectric film on an oxide semiconductor for ferroelectric field-effect transistors (FeFETs).