High-pressure Annealing Process Research Articles

Oxygen Vacancy Control as a Strategy to Enhance Imprinting Effect in Hafnia Ferroelectric Devices

Hafnia-based ferroelectric materials are recently drawing a significant attention for future electronic devices; however, there is a need to further enhance their functionality for practical applications. Especially, an imprinting effect has been regarded as a defect to be reduced in ferroelectrics; yet, it can be positively applied to various electronic devices with the functionality of self-rectifying behavior and threshold voltage adjustment. For the first time, we report a high imprinting effect in bilayer stack capacitors [TiN/Hf0.5Zr0.5O2 (HZO)/tantalum oxide (TaO)/TiN] by employing an optimal TaO insertion layer. Furthermore, the imprinting effect was enhanced by adopting high-pressure annealing (HPA) process. X-ray photoelectron spectroscopy (XPS) depth profile analysis reveals that the origin of the imprint field is the tantalum suboxides (Ta2O5-x) with doubly positively charged oxygen vacancies ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\text {o}}^{++}$ </tex-math></inline-formula> ). The imprint field increases with increasing HPA temperatures and achieved a high imprint field of 1.65 MV/cm at 600 °C. Moreover, endurance was observed up to 108 cycles without a breakdown while maintaining the original coercive fields up to 105 cycles. We also investigated how the TaO insertion layer with an imprint field influences the switching, interfacial, and ferroelectric properties. These findings on the imprinting effect provide a new strategy to improve the functionality of hafnia-based ferroelectric devices in the near future.

Low-thermal-budget (300 °C) ferroelectric TiN/Hf0.5Zr0.5O2/TiN capacitors realized using high-pressure annealing

In this Letter, a high-pressure annealing (HPA) process is proposed as a way to reduce the thermal budget of Hf0.5Zr0.5O2 (HZO) thin films with ferroelectric behaviors. The low-thermal-budget process is essential for integrating ferroelectric devices in the back-end-of-line to provide more functionalities and effective memory area. For the HZO film annealed at 300 °C using the HPA process, an orthorhombic phase responsible for ferroelectric behavior was formed with a decrease in film thickness, resulting in a remanent polarization (Pr) of ∼13 μC/cm2 (i.e., 2Pr of ∼26 μC/cm2). Meanwhile, when only the annealing time was increased at 300 °C without applying pressure, the HZO film did not crystallize and exhibited linear dielectric properties. Consequently, the HZO films (&amp;lt;10 nm) can be crystallized by applying pressure (15 atm) even at low temperatures of 300 °C, thereby obtaining ferroelectric properties.

Effects of high pressure oxygen annealing on Hf0.5Zr0.5O2 ferroelectric device

We report a high-pressure oxygen annealing (HPOA) process to improve the performance of TiN/Hf0.5Zr0.5O2 (HZO)/TiN devices by controlling the number of oxygen vacancies and carbon contaminants. The ferroelectric properties of HZO film after HPOA at 250 °C for 30 min under different oxygen pressures from 0 to 80 bar were evaluated by electrical and structural characterizations. We found that a sample treated with an oxygen pressure at 40 bar exhibited large switchable polarization (2Pr) of approximately 38 and 47 μC cm−2 in its pristine and wake-up states, respectively. Compared to a control sample, an approximately 40% reduction in the wake-up effect was achieved after HPOA at 40 bar. Improved ferroelectric properties of HZO film can be explained by the appropriate amount of oxygen vacancies and reduced carbon contaminants after HPOA.

Excellent Reliability and High-Speed Antiferroelectric HfZrO2 Tunnel Junction by a High-Pressure Annealing Process and Built-In Bias Engineering

Hafnia-based ferroelectric tunnel junctions (FTJs) have great potential for use in logic in nonvolatile memory because of their complementary metal-oxide-semiconductor process compatibility, low power consumption, high scalability, and nondestructive readout. However, typically, ferroelectrics have a depolarization field, resulting in poor endurance owing to the early dielectric breakdown. Herein, an outstandingly reliable and high-speed antiferroelectric HfZrO tunnel junction (AFTJ) is probed to understand whether it is a promising candidate for next-generation nonvolatile memory applications. High-reliability AFTJ can be explained by less charge injection due to the low depolarized field. The formation of two stable nonvolatile states, even with antiferroelectric materials, is possible if asymmetric work function electrodes and fixed oxide charges are employed, generating a built-in bias and shifting the polarization-voltage curve. In addition, via high-pressure annealing, a critical voltage that determines the transition from the t-phase to the o-phase is effectively reduced (22%). The AFTJ shows a higher endurance property (>109 cycles) and faster switching speed (<30 ns) than FTJ. Hence, it is proposed that with the help of internal bias modulation and high-pressure annealing, AFTJs can be employed in next-generation memory devices.

Strong enhancement of spin ordering byA-site magnetic ions in the ferrimagnetCaCu3Fe2Os2O12

$AB{\mathrm{O}}_{3}$ perovskite is a kind of very important functional material with versatile physical properties. Although $B$-site chemical substitution with various magnetic ions has been widely investigated, the $A$-site doping with magnetic transition metal is little known. Here we report $A{A}_{3}^{\ensuremath{'}}{B}_{2}{B}_{2}^{\ensuremath{'}}{\mathrm{O}}_{12}$-type $A$- and $B$-site ordered ferrimagnet $\mathrm{CaC}{\mathrm{u}}_{3}\mathrm{F}{\mathrm{e}}_{2}\mathrm{O}{\mathrm{s}}_{2}{\mathrm{O}}_{12}$ with magnetic transition metals occupying three different atomic sites (${A}^{\ensuremath{'}}, B$, and ${B}^{\ensuremath{'}}$ sites). This compound is synthesized by a special high-pressure annealing process. It possesses a much higher Curie temperature ${T}_{\mathrm{C}}$ of 580 K compared with that of the $B$-site-only ordered $\mathrm{C}{\mathrm{a}}_{2}\mathrm{FeOs}{\mathrm{O}}_{6}$ (${T}_{\mathrm{C}}=320\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) without magnetic ion at the $A$ site. First-principles numerical calculations reveal that this enhancement primarily originates from the additional spin interaction between the ${A}^{\ensuremath{'}}$-site $\mathrm{C}{\mathrm{u}}^{2+}$ and the ${B}^{\ensuremath{'}}$-site $\mathrm{O}{\mathrm{s}}^{5+}$, generating a strong $\mathrm{C}{\mathrm{u}}^{2+}(\ensuremath{\uparrow})\mathrm{F}{\mathrm{e}}^{3+}(\ensuremath{\uparrow})\mathrm{O}{\mathrm{s}}^{5+}(\ensuremath{\downarrow})$ ferrimagnetic spin coupling. This work opens up an alternative way for enhancing the spin ordering temperature by introducing $A$-site magnetic ions.

Effects of structural modification via high-pressure annealing on solution-processed InGaO films and thin-film transistors

We investigated the structural modification of solution-processed nanocrystalline InGaO films via high-pressure annealing and fabricated thin-film transistors. The grain size of InGaO films annealed in the presence of oxygen under high pressure was significantly changed compared the films annealed without high pressure ambient. The O1s XPS peak distribution of InGaO films annealed under high pressure at 350 °C showed a peak similar to that of the non-pressure annealed film at 500 °C. The high-pressure annealing process promoted the elimination of organic residues and dehydroxylation of the metal hydroxide (M–OH) complex. We confirmed the improved device performance of high-pressure annealed InGaO-based thin-film transistors owing to the reduction in charge-trap density.

Hydrogenated IGZO Thin-Film Transistors Using High-Pressure Hydrogen Annealing

Hydrogenation of thin-film indium-gallium-zincoxide (IGZO) is carried out by applying a high-pressure hydrogen annealing (HPHA) process under 5-atm pressure at different temperatures of 260°C, 270°C, and 280°C. The HPHA effectively increases the carrier concentration and the Hall mobility up to ~ 1019 cm-3 and ~ 6.4 cm2/Vs, respectively. The HPHA-IGZO films exhibit smoother surfaces as compared with the as-grown films. The HPHA performs at a temperature of 260 °C that greatly enhances the electrical characteristics of IGZO TFTs, leading to a saturation field effect mobility of 7.4 cm2/Vs, a subthreshold slope of 0.37 V/decade, a threshold voltage of 2.2 V, and an ION/IOFF of 2.0×106.

Effect of Hydrogen on Vacancy Formation in Sputtered Cu Films Studied by Positron Annihilation Spectroscopy

As a part of the LSI interconnect fabrication process, a post-deposition high-pressure annealing process is proposed for embedding copper into trench structures. The embedding property of sputtered Cu films has been recognized to be improved by adding hydrogen to the sputtering argon gas. In this study, to elucidate the effect of hydrogen on vacancy formation in sputtered Cu films, normal argon-sputtered and argon–hydrogen-sputtered Cu films were evaluated by positron annihilation spectroscopy. As a result, monovacancies with a concentration of more than 10-4 were observed in the argon–hydrogen-sputtered Cu films, whereas only one positron lifetime component corresponding to the grain boundary was detected in the normal argon-sputtered Cu films. This result means monovacancies are stabilized by adding hydrogen to sputtering gas. In the annealing process, the stabilized monovacancies began clustering at around 300 °C, which indicates the dissociation of monovacancy-hydrogen bonds. The introduced monovacancies may promote creep deformation during high-pressure annealing.

Reflow Phenomenon Analysis of Large Scale Integrated Cu Interconnections in Via Holes by Viscoelastic Deformation Simulation

The reflow phenomenon of Cu interconnections deposited over via holes was analyzed by viscoelastic deformation simulation using a finite-element method to clarify the embedding mechanism of Cu interconnections into via holes in a novel dual-damascene fabrication technology, which combined sputter deposition and high-pressure annealing. Cu is considered to be a viscoelastic body, and the stress distribution and deformation behavior of Cu interconnections were calculated. As a result, the deformation behavior of the Cu interconnections exhibited close agreement between the calculated and the observed values. From our series of results, we inferred that Cu interconnections are embedded into via holes by the creep deformation mechanism defined in this study during the high-pressure annealing process.

Effects of gate insulator using high pressure annealing on the characteristics of solid phase crystallized polycrystalline silicon thin-film transistors

The oxidizing ambient was built using high pressure H2O vapor at 550 °C. For the solid phase crystallization (SPC) polycrystalline silicon (poly-Si) that is annealed for 1 h at 2 MPa, the oxide thickness is about 150 Å. The oxide layer is approximately 90 Å above the original surface of the poly-Si and 60 Å below the original surface. The oxide layer is used as the first gate insulator layer of thin-film transistors (TFTs). The heating at 550 °C with 2 MPa H2O vapor increased the carrier mobility from 17.6 cm2/V s of the conventional SPC process to 30.4 cm2/V s, and it reduced the absolute value of the threshold voltage (Vth) from 4.13 to 3.62 V. The subthreshold swing also decreased from 0.72 to 0.60 V/decade. This improvement is attributed mainly to the reduction in defect density at the oxide/poly-Si interface and in the poly-Si film by the high pressure annealing (HPA) process. Since the realization of excellent performance at the oxide/poly-Si interface and in poly-Si depends on the defect density, the poly-Si having the thermal oxide formed by a combined process of SPC and HPA may be well suited for fabrication of poly-Si TFTs for flat panel displays such as active matrix organic light emitting diodes.

Pressure-induced electrical and structural anomalies in Pb1−xCaxTiO3 thin films grown at various oxygen pressures by chemical solution route

Lead calcium titanate (Pb1−xCaxTiO3 or PCT) thin films have been thermally treated under different oxygen pressures, 10, 40 and 80 bar, by using the so-called chemical solution deposition method. The structural, morphological, dielectric and ferroelectric properties were characterized by x-ray diffraction, FT-infrared and Raman spectroscopy, atomic force microscopy and polarization–electric-field hysteresis loop measurements. By annealing at a controlled pressure of around 10 and 40 bar, well-crystallized PCT thin films were successfully prepared. For the sample submitted to 80 bar, the x-ray diffraction, Fourier transformed-infrared and Raman data indicated deviation from the tetragonal symmetry. The most interesting feature in the Raman spectra is the occurrence of intense vibrational modes at frequencies of around 747 and 820 cm−1, whose presence depends strongly on the amount of the pyrochlore phase. In addition, the Raman spectrum indicates the presence of symmetry-breaking disorder, which would be expected for an amorphous (disorder) and mixed pyrochlore–perovskite phase. During the high-pressure annealing process, the crystallinity and the grain size of the annealed film decreased. This process effectively suppressed both the dielectric and ferroelectric behaviour. Ferroelectric hysteresis loop measurements performed on these PCT films exhibited a clear decrease in the remanent polarization with increasing oxygen pressure.

Effects of high pressure annealing on the characteristics of solid phase crystallization poly-Si thin-film transistors

Integrating circuits into organic light emitting diode displays require fabrication of polycrystalline silicon (poly-Si) based thin-film transistors (TFTs) on glass substrates. In this work we evaluated the use of high pressure annealing (HPA) process of poly-Si films in H2O atmosphere to improve TFT characteristics via reducing defect density in poly-Si films. We attempted to develop a HPA process at temperatures below 600°C without causing any glass distortion and reducing the throughput. The HPA-treated poly-Si film was analyzed using various spectroscopic methods such as Raman, x-ray photoelectron spectroscopy, and transmission electron microscope, and the evaluation of the characteristics of TFTs fabricated by such poly-Si films was made. The heating at 550°C with 1MPa H2O vapor increased the carrier mobility from 8.5to20cm2∕Vs and reduced the absolute value of the threshold voltage from 9.6to6.5V, as compared with the conventional solid phase crystallization (SPC) process. The sub-threshold swings also decreased from 1.2to0.8V/decade. Since the realization of good performance in poly-Si depends on the defect density, the poly-Si formed by a combined process of SPC and HPA may be well suited for fabrication of poly-Si TFTs for flat panel displays such as liquid crystal display and active matrix organic light emitting diode that require circuit integration on panels.

Effects of the high-pressure annealing process on the reflow phenomenon of copper interconnections for large scale integrated circuits

The embedding effect of physical vapour deposited and electrochemical deposited copper films due to a high-pressure annealing process at 400 °C and 150 MPa was investigated in order to apply this high-pressure annealing process to dual-damascene fabrication technology for copper interconnections. The experimental results support a thermal elasticity and plasticity analysis using a finite-element method which predicts that additional external pressure acts to push copper films to the via holes. This analytical result agrees well with the hole filling performance under the high-pressure annealing of test element group specimens on which via holes of 0.28 μm in diameter and 1.2 μm in depth were previously formed. The residual stress left after lowering the temperature and pressure has no dependence on the additional external pressure and therefore does not reduce the reliability of the copper interconnections. However, the additional external pressure reduces the incremental creep strain of copper during the heating and holding step and reduces the stress transition point during the cooling step. This indicates that the additional external pressure on annealing at approximately 400 °C is effective for the perfect filling of copper into via holes without minute voids and in suppressing the siphoning phenomenon in copper from via holes.

Ferroelectric Lead Zirconate Titanate Thin Films Synthesized via a High-Pressure Crystallization Process

The crystallization of lead zirconate titanate (PZT) thin films derived from amorphous precursor films has been significantly enhanced using a high-pressure crystallization (HPC) process. By annealing at around 16.5 MPa, well-crystallized PZT thin films were successfully prepared at temperature as low as 350°C which is several hundred degrees centigrade lower than that in the conventional atmospheric annealing process. This novel process considerably reduced the thermal budget and the energy consumption during film processing. During the high-pressure annealing process, the crystallinity and grain size of the annealed films increased with higher annealing temperature and longer annealing time. This developed process effectively suppressed both the outward diffusion of lead species from PZT films into the substrate region and the diffusion of titanium species from the bottom electrodes into the silicon layers. This is because the low annealing temperatures adopted in the high-pressure process reduced the mobility and diffusion rate of the constituent species.

Application of an electron backscatter diffraction pattern to Cu damascene-fabricated interconnections filled by a high-pressure anneal process

The microstructure of Cu interconnections fabricated by high-pressure annealing was evaluated using a field emission scanning electron microscope/electron backscatter diffraction pattern (FE-SEM/EBSP) technique, and the results are compared with as-deposited and normally annealed Cu films. The results show some grains extending from the bulk field to the via regions in the case of the high-pressure annealed Cu films. The existence of via holes was also observed, in which all grains were (111) oriented. This indicates that the high-pressure annealing process enables the Cu that in-fills the via holes to develop into favorable microstructures, i.e., single-crystal and with (111) orientation.

Application of High-pressure Annealing Process to Dual Damascene Copper Interconnections

We have carried out a detailed study of the relevant process techniques by using high-pressure annealing in order to embed Cu interconnections flawlessly into via holes or trenches, and have thereby identified a process technique increase the reliability of electrical circuits. In th e present study, Cu interconnections were subjected to heat treatment in a high-pressure argon gas atmosphere (150 MPa) with the prospect that such a process might lead to optimized conditions for creating the embedded Cu interconnection by preventing the occurrence of minute voids, improving the distribution of poly-crystalline orientation and improving the adhesive strength between Cu and TaN (barrier layers), thereby increasing the reliability of Cu interconnections and consequently improve the yield. This paper describes the effects of the high-pressure annealing process for dual damascene Cu interconnections in some detail.