Phase Of HfO2 Research Articles

Reliability assessment of ultra-thin HfO2 films deposited on silicon wafer

Ultra-thin hafnium dioxide (HfO2) is used to replace silicon dioxide to meet the required transistor feature size in advanced semiconductor industry. The process integration compatibility and long-term reliability for the transistors depend on the mechanical performance of ultra-thin HfO2 films. The criteria of reliability including wear resistance, thermal fatigue, and stress-driven failure rely on film adhesion significantly. The adhesion and variations in mechanical properties induced by thermal annealing of the ultra-thin HfO2 films deposited on silicon wafers (HfO2/SiO2/Si) are not fully understood. In this work, the mechanical properties of an atomic layer deposited HfO2 (nominal thickness ≈10nm) on a silicon wafer were characterized by the diamond-coated tip of an atomic force microscope and compared with those of annealed samples. The results indicate that the annealing process leads to the formation of crystallized HfO2 phases for the atomic layer deposited HfO2. The HfSixOy complex formed at the interface between HfO2 and SiO2/Si, where the thermal diffusion of Hf, Si, and O atoms occurred. The annealing process increases the surface hardness of crystallized HfO2 film and therefore the resistance to nano-scratches. In addition, the annealing process significantly decreases the harmonic contact stiffness (or thereafter eliminate the stress at the interface) and increases the nano-hardness, as measured by vertically sensitive nano-indentation. Quality assessments on as-deposited and annealed HfO2 films can be thereafter used to estimate the mechanical properties and adhesion of ultra-thin HfO2 films on SiO2/Si substrates.

Atomic scale observation of phase separation and formation of silicon clusters in Hf higk-κ silicates

Hafnium silicate films were fabricated by RF reactive magnetron sputtering technique. Fine microstructural analyses of the films were performed by means of high-resolution transmission electron microscopy and atom probe tomography. A thermal treatment of as-grown homogeneous films leads to a phase separation process. The formation of SiO2 and HfO2 phases as well as pure Si one was revealed. This latter was found to be amorphous Si nanoclusters, distributed uniformly in the film volume. Their mean diameter and density were estimated to be about 2.8 nm and (2.9 ± 0.4) × 1017 Si-ncs/cm3, respectively. The mechanism of the decomposition process was proposed. The obtained results pave the way for future microelectronic and photonic applications of Hf-based high-κ dielectrics with embedded Si nanoclusters.

Hafnia-Based Luminescent Insulator for Phosphor Applications

Pure and doped hafnia-based films were fabricated by RF magnetron sputtering and their microstructure, optical and luminescent properties were investigated versus annealing treatment. It was observed a phase separation in Si-rich-HfO2 films at 900-1100°C resulted in the formation of HfO2 and SiO2 phases, as well as pure silicon clusters. A light emission in the orange-red spectral range was observed from Si-rich-HfO2 samples contrary to their pure counterparts. The correlation of the peak position of red photoluminescence with silicon cluster sizes allowed gives the evidence of the carrier recombination in silicon clusters. The comparison of Er-doped-HfO2 and Er-doped Si-rich-HfO2 films showed an enhancement of rare-earth emission efficiency due to an effective energy transfer from Si-clusters.

Fabrication and plasma arc thermal shock resistance of HfB2-based ultra high temperature ceramics

Two hafnium diboride based ceramic matrix composites containing 20% (volume fraction) SiC particle and with or without AlN as sintering additives were fabricated by hot-pressed sintering. The mechanical properties and microstructures of these two composites were tested and the thermal shock resistances were evaluated by plasma arc heater. The results indicate that the composite with AlN as sintering additive has a denser and finer microstructure than composite without sintering additive, and the mechanical properties, thermal shock resistance of the composite with AlN as sintering additive are also higher than those of the composite without AlN. Microstructure analysis on the cross-section of two composites after thermal shock tests indicates that a compact oxidation scale contains HfO2 and Al2O3 liquid phase is found on the surface of composite with AlN, which could fill the voids and cracks of surface and improve the thermal shock resistance of composite.

Nitridation of atomic-layer-deposited HfO2/Al2O3 stacks by NH3 annealing

HfO2/Al2O3 stacks are grown on Si (100) substrate by atomic layer deposition and then nitridized using ammonia (NH3) annealing in the temperature range of 600–900°C. The effects of NH3 annealing temperature on the structural and physical properties are investigated. HfO2 phase changes from monoclinic to orthorhombic with the annealing treatment. Moreover, the increasing of the grain size and decreasing of the valence band maximum with increasing annealing temperature are demonstrated. In addition, the film annealed at 900°C clearly shows that there exists an amorphous Al2O3 layer between partially crystalline HfO2 layer and the Si substrate.

Response to “Comment on ‘Unusual Photoluminescence of CaHfO3 and SrHfO3 Nanoparticles’”

The comment from Clavel et al. on our paper entitled “Unusual photoluminescence of CaHfO3 and SrHfO3 nanoparticles” raises questions on the synthesis, the photoluminescence, and the structure of these perovskite nanoparticles. The comment is based on several references used as support; most of which are self-citations. It surprisingly seems to miss the key point of our report, i.e., no luminescence from regular hafnia perovskite nanoparticles is expected under the experimental conditions described in our work, as there are no energy levels available for any radiative processes in contrast to many lanthanide and rare earth (RE) compounds. This is the reasoning behind entitling the observed strong visible luminescence as “unusual” and suggesting a surface-related effect as its plausible origin. We find the comment rather dubious, and at times unrealistic and inconsistent. More specifically, the authors open their comment by claiming that the photoluminescence (PL) studied in our paper is not a surface-related effect. However, in their conclusion, they self-contradictorily suggest that the PL observed in our study is related to benzoate species adsorbed on the surface of the nanoparticles, which in our opinion is a surface related effect. If the authors had contacted us directly, we would have been equally glad to answer their concerns. With respect to the perovskite phase: The structure of these hafnia perovskites was studied using Cs corrected TEM and synchrotron measurements. An X-ray diffraction (XRD) pattern of CaHfO3 sample fitted with Rietveld refinement (Figure 1a) highlights the XRD peaks of the perovskite structure and provides sizes <2 nm for the perovskite particles (smallest perovskites ever synthesized in the literature) and 6 nm for the HfO2. A size decrease induces peak broadening for the perovskite phase; the secondary cubic HfO2 phase (nanoparticles of average size ≈5–6 nm) then becomes more prominent on the XRD pattern. This explains why, the authors had incorrectly considered the XRD pattern to correspond to the HfO2 cubic phase. The authors have expressed disappointment in not seeing the XRD pattern of SrHfO3 in our paper; we have therefore included a synchrotron XRD pattern, in Figure 1b, which validates the

The effect of oxygen flow rates on magnetic and high‐frequency characteristics of Fe‐Hf‐O films

AbstractThis study aimed to investigate the influence of oxygen flow rate on magnetic and high‐frequency properties of as‐deposited FeHfO thin films, which were fabricated by DC reactive magnetron sputtering in an Ar + O2 atmosphere. These films exhibited mixed phases of α‐Fe nanograins and amorphous HfO2 phase, showing nanocrystalline structure and soft magnetic properties. The dispersion character of FeHfO films changed from relaxation‐type to resonance‐type when the oxygen flow rate varied from 1.0 to 1.2 sccm. Furthermore, the Fe58.8Hf13.1O28.1 film with the optimum O2 flow rate of 1.2 sccm exhibited high saturation magnetization of 10.6 kG, a high resistivity of 258 µΩ cm, a real component of permeability (µ′) of 250 up to 1 GHz and a high ferromagnetic resonance frequency of 2.5 GHz. It is expected that this film should be promising for practical applications as a high‐frequency ferromagnetic material.

Laser-deposited thin hafnium dioxide condensates: Electron-microscopic study

Thin films of hafnium dioxide (HfO2) have been obtained by pulsed laser ablation of hafnium targets in oxygen atmosphere and characterized by transmission electron microscopy and electron diffraction. Conditions ensuring the formation of an amorphous phase, tetragonal and monoclinic modifications of HfO2 have been determined. It is established that the crystalline phase is formed on orienting substrates at lower temperatures than on neutral ones. The phenomenon of epitaxy has been observed for tetragonal modification of HfO2. Annealing in air leads to crystallization of an initially amorphous film with the formation of a monoclinic HfO2 modification.

Dependence of optimized annealing temperature for tetragonal phase formation on the Si concentration of atomic-layer-deposited Hf-silicate film

This study examined the relation between the permittivity and microstructures of atomic layer deposited Hf1−xSixO2 (HfSiO) thin films with different Si concentrations as a function of post-deposition annealing (PDA) temperature. The PDA at high temperature results in the separation of crystallized HfO2 phase from the much higher Si-containing amorphous-like matrix. Tetragonal phase HfO2 formation with higher permittivity than the monoclinic HfO2 phase is induced with an appropriate Si concentration in the film (∼10–20%). In the crystallized HfSiO film, the Si concentration in the phase-separated HfO2 (mainly consisting of HfO2) could be controlled by PDA temperature, which determines the degree of phase separation. The increased PDA temperature reduces the Si concentration in the phase-separated HfO2, which induced monoclinic phase formation. Therefore, the PDA temperature for maximized permittivity of the crystallized HfSiO films (maximized tetragonal phase portion in the film) depends on the Si concentration of the HfSiO film in the as-deposited state.

Synthesis and characterization of nanometric yttrium-doped hafnia solid solutions

Nanometric-sized yttrium doped HfO2 powders were obtained by applying metathesis and combustion reactions. The tailored composition of solid solutions was: Hf1−xYxO2−δ with concentration “x” ranging from 0 to 0.2. HfCl4 was used as a source of hafnium whereas Y(NO3)3·6H2O was used as a source of yttrium. The obtained powders were annealed at different temperatures in order to induce crystallization of HfO2. The influence of dopant concentration, annealing temperature and annealing time on powder properties was examined. The XRD analysis revealed that the crystal structure of HfO2 depends on the dopant concentration. The samples doped with 20 mol% of yttrium and annealed at 1500 °C had high-temperature, cubic structure even after cooling to room temperature. The presence of relatively large amount of dopant was beneficial in stabilizing highly desirable cubic phase of HfO2. It was found that the crystallite size lies in the nanometric range (<10 nm).

Study on atomic and electronic structures of ceramic materials using spectroscopy, microscopy, and first principles calculation

In this review, following two topics are introduced: 1) experimental and theoretical electron energy loss (EEL) near edge structures (ELNES) and X-ray absorption near edge structures (XANES), and 2) atomic and electronic structure analysis of ceramic interface by combing spectroscopy, microscopy, and first principles calculation. In the ELNES/XANES calculation, it is concluded that inclusion of core-hole effect in the calculation is essential. By combining high energy resolution observation and theoretical calculation, detailed analysis of the electronic structure is achieved. In addition, overlap population (OP) diagram is used to interpret the spectrum. In the case of AlN, sharp and intense first peak of N-K edge is found to reflect narrow dispersion of the conduction band bottom. By applying ELNES and the OP diagram to Cu/Al2O3 heterointerface, it is revealed that intensity of prepeak in O-K edge is inverse proportional to interface strength. The relationships between atomic structure and defect energetics at SrTiO3 grain boundary are also investigated, and reveal that the formation behavior of Ti vacancy is sensitive to the structural distortion. In addition, by using state-of-the-art spectroscopy, microscopy, and first principles calculations, atomic scale visualization of fluorine dopant in LaFeOAs and first principles calculation of HfO2 phase transformation are demonstrated.

Effects of physical growth conditions on the structural and optical properties of sputtered grown thin HfO 2 films

HfO 2 thin films were prepared by reactive DC magnetron sputtering technique on (100) p-Si substrate. The effects of O 2/Ar ratio, substrate temperature, sputtering power on the structural properties of HfO 2 grown films were studied by Spectroscopic Ellipsometer (SE), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrum, and X-ray photoelectron spectroscopy (XPS) depth profiling techniques. The results show that the formation of a SiO x suboxide layer at the HfO 2/Si interface is unavoidable. The HfO 2 thickness and suboxide formation are highly affected by the growth parameters such as sputtering power, O 2/Ar gas ratio during sputtering, and substrate temperature. XRD spectra show that the deposited films have (111) monoclinic phase of HfO 2, which is also supported by FTIR spectra. XPS depth profiling spectra shows that highly reactive sputtered Hf atoms consume some of the oxygen atoms from the underlying SiO 2 to form HfO 2, leaving Si–Si bonds behind.

Effect of Annealing on the Interfacial and Structural Properties of Amorphous Silicon-Hafnia Films

Chemical and physical properties of the interface formed between amorphous silicon (a-Si) and hafnium oxide (HfO2) were investigated using X-ray reflectivity (XRR) and X-ray photoelectron spectroscopy (XPS). XRR showed that the interface layer formed between the a-Si and HfO2 layer had a thickness of 0.7 ± 0.3 nm and a density of 4.4 ± 0.2 g/cm3. Based on the XPS results, the interface comprised HfO2, silicon oxide, and hafnium silicate phases. High-temperature annealing led to the conversion of elemental silicon and nonstoichiometric silicate into silicon dioxide phases. This reaction was also accompanied by the chemical reduction of the HfO2 phase. Annealed films crystallized into the monoclinic phase of HfO2 with a preferred orientation along the (111) axis.

ChemInform Abstract: Pressure-Induced Phase Transformation of HfO2.

The pressure dependence of the Raman spectra of HfO2 was measured by a micro-Raman technique using a singlecrystal specimen in the pressure range from 0 to 10 GPa at room temperature. The symmetry assignment of Raman bands of the monoclinic phase was experimentally accomplished from the polarization measurements for the single crystal. With increased pressure, a phase transformation for the monoclinic phase took place at 4.3 ± 0.3 GPa. Nineteen Raman bands were observed for the high-pressure phase. The spectral structure of the Raman bands for the high-pressure phase was similar with those reported previously for ZrO2. The space group for the high-pressure phase of HfO2 was determined as Pbcm, which was the same as that of the high-pressure phase for ZrO2 on the basis of the number and the spectral structure of the Raman bands.

Cubic phase stabilization and improved dielectric properties of atomic-layer-deposited EryHf1-yOx thin films

The electrical and physical properties of atomic-layer-deposited EryHf1-yOx thin films have been investigated with different stoichiometries of erbium oxide (Er2O3) and hafnium oxide (HfO2). The as-deposited and annealed EryHf1-yOx films exhibit much higher dielectric constants than the reported k-values of the corresponding binary oxides. The highest k-value of 37.6 ± 1 is achieved with 13 at.% of erbium in the film. The enhancement in dielectric constant is due to the formation of the cubic HfO2 phase stabilized by erbium, as revealed by x-ray diffraction experiments. The annealed mixed oxide films exhibit remarkably low oxide charges, low interface states, low leakage, and good breakdown electric fields.

Structure, optical properties and thermal stability of pulsed sputter deposited high temperature HfO x/Mo/HfO 2 solar selective absorbers

Solar selective coatings of HfO x /Mo/HfO 2 were deposited on copper (Cu) and stainless steel (SS) substrates using a magnetron sputtering system. The HfO x and HfO 2 layers were deposited from the sputtering of Hf target in Ar+O 2 plasma using an asymmetric bipolar-pulsed direct current generator, whereas the Mo layer was deposited from the sputtering of Mo target in the Ar plasma. The optimized HfO x /Mo/HfO 2 multilayer absorber on Cu substrate exhibited high solar absorptance ( α=0.905–0.923) and low thermal emittance ( ε 82 °C =0.07–0.09). Similarly, on SS substrates the optimized coatings exhibited α and ε 82 °C in the ranges of 0.902–0.917 and 0.15–0.17, respectively. The X-ray diffraction data showed that the HfO x /Mo/HfO 2 coating consists of tetragonal and monoclinic phases of HfO 2, which was confirmed by micro-Raman spectroscopy data. The bonding structure of the HfO x and the HfO 2 layers were confirmed using X-ray photoelectron spectroscopy data. The optical constants ( n and k), measured using spectroscopic ellipsometry, showed that the top HfO 2 layer acts as an antireflection coating and the bottom two layers (HfO x and Mo) are the main absorber layers. The analysis of the spectroscopic ellipsometric data indicated that the band gap of HfO x and HfO 2 layers were 3.90 and 5.82 eV, respectively, indicating non-stoichiometric nature of HfO x . In order to study the thermal stability of the HfO x /Mo/HfO 2 coatings, they were subjected to heat treatment in air and vacuum at different temperatures ( T A). The HfO x /Mo/HfO 2 coatings deposited on Cu substrates were thermally stable up to 400 °C for 2 h in air. Addition of a thin Mo interlayer (40 nm) in the HfO x /Mo/HfO 2 coating (i.e., Mo/HfO x /Mo/HfO 2) deposited on Cu substrates exhibited high solar selectivity ( α/ ε) of 0.872/0.09 even after heat-treatment in air up to 500 °C for 2 h. At T A=525 °C, the solar selectivity decreased drastically ( α/ ε=0.761/0.35) due to the formation of MoO 2, MoO 3 and HfMo 2O 8 phases. The Mo/HfO x /Mo/HfO 2 coatings deposited on SS substrates showed no significant changes in α and ε values after annealing at 500 °C in air and at 800 °C in vacuum. These results were confirmed by micro-Raman spectroscopy measurements, which showed the compositional stability of these coatings up to 500 °C in air and 800 °C in vacuum.

(Invited) Dielectric Properties and Flat-Band Voltages of Doped- HfO2 Thin Films

The control of high-symmetry phases of HfO2 can be achieved by cationic substitution for Hf. The electrical properties of the cubic HfO2 phase stabilized by addition of yttrium or magnesium were investigated. The introduction of moderate Y or Mg doping content (~10-15%) in HfO2 results in an enhancement of the dielectric constant. No degradation of the interface state density and of the leakage current was noticed. The flat-band voltage is shifted to positive voltages, similarly as it was observed for monoclinic and cubic pure HfO2 thin films. This result confirms that the contribution of the SiO2/high-k interface to the flat-band voltage depends on the structural interface properties.

Synthesis and characterization of HfO 2 and ZrO 2 thin films deposited by plasma assisted reactive pulsed laser deposition at low temperature

A plasma assisted reactive pulsed laser deposition process was demonstrated for low-temperature deposition of thin hafnia (HfO 2) and zirconia (ZrO 2) films from metallic hafnium or zirconium with assistance of an oxygen plasma generated by electron cyclotron resonance microwave discharge. The structure and the interface of the deposited films on silicon were characterized by means of Fourier transform infrared spectroscopy, which reveals the monoclinic phases of HfO 2 and ZrO 2 in the films with no interfacial SiO x layer between the oxide film and the Si substrate. The optical properties of the deposited films were investigated by measuring the refractive indexes and extinction coefficients with the aid of spectroscopic ellipsometry technique. The films deposited on fused silica plates show excellent transparency from the ultraviolet to near infrared with sharp ultraviolet absorption edges corresponding to direct band gap.

Formation of Anatase Phase in HfO2in Tensile Stress: AnAb InitioStudy

We report a direct computational evidence of a phase transformation from the baddeleyite phase to an anatase-like phase in HfO2 with the application of tensile stress. The phase transformation is first order and associated with the shear deformation. The energy–volume calculations indicate that the energetics of the anatase crystal is favorable and the baddeliyite-to-anatase phase transformation occurs −1.0 GPa, implying that the anatase-like phase of HfO2 can be grown experimentally as thin films under tensile strain.

Synthesis and characterization of hafnium oxide films for thermo and photoluminescence applications

Hafnium oxide (HfO(2)) films were deposited by the ultrasonic spray pyrolysis process. The films were synthesized from hafnium chloride as raw material in deionized water as solvent and were deposited on corning glass substrates at temperatures from 300 to 600 degrees C. For substrate temperatures lower than 400 degrees C the deposited films were amorphous, while for substrate temperatures higher than 450 degrees C, the monoclinic phase of HfO(2) appeared. Scanning electron microscopy showed that the film's surface resulted rough with semi-spherical promontories. The films showed a chemical composition close to HfO(2), with an Hf/O ratio of about 0.5. UV radiation was used in order to achieve the thermoluminescent characterization of the films; the 240 nm wavelength induced the best response. In addition, preliminary photoluminescence spectra, as a function of the deposition temperatures, are shown.