Morphology, composition and thermal stability of thin SiO2/HfO2 layers grown on silicon by electron-beam evaporation in vacuum

The results of integrated studies of thin-film structures based on silicon and hafnium dioxides on silicon grown by electron-beam evaporation in vacuum are presented. The surface morphology, structural and phase composition of these films depending on the annealing temperature within 500–1100°C are studied. Special consideration is given to the change in the state of the interfaces after annealing. It is determined that annealing in a flow of nitrogen with the addition of oxygen (～10 vol %) at 700°C does not lead to structural and phase changes in the films, but the intensity of the electron paramagnetic resonance (EPR) spectra of uncompensated bonds on the HfO₂-Si interface decreased. Annealing at higher temperatures stimulates crystallization of the HfO₂ films and hafnium silicate is formed on the SiO₂-HfO₂ interface and suboxide SiO _x appears on the HfO₂-Si interface.     

Effect of Annealing Temperature on Structural and Optical Properties of N-Doped ZnO Films

Nitrogen-doped ZnO （ZnO：N） films are prepared by thermal oxidation of sputtered Zn3N2 layers on A1203 substrates. The correlation between the structural and optical properties of ZnO：N films and annealing temperatures is investigated. X-ray diffraction result demonstrates that the as-sputtered Zn3N2 films are transformed into ZnO：N films after annealing above 600℃. X-ray photoelectron spectroscopy reveals that nitrogen has two chemical states in the ZnO：N films： the No acceptor and the double donor （N2）o. Due to the No acceptor, the hole concentration in the film annealed at 700℃ is predicted to be highest, which is also confirmed by Hall effect measurement. In addition, the temperature dependent photoluminescence spectra allow to calculate the nitrogen acceptor binding energy.     

Influence of Ytterbia Content on Residual Stress and Microstructure of Y2O3--ZrO2 Thin Films Prepared by EB-PVD

Y2O3 stabilized ZrO2 （YSZ） thin films with different Y2O3 molar contents （0, 3, 7, and 12 mol%） are deposited on BK7 substrates by electron-beam evaporation technique. The effects of different Y2O3 contents on residual stresses and structures of YSZ thin films are studied. Residual stresses are investigated by means of two different techniques： the curvature measurement and x-ray diffraction method. It is found that the evolution of residual stresses of YSZ thin films by the two different methods is consistent. Residual stresses of films transform from compressive stress into tensile stress and the tensile stress increases monotonically with the increase of Y2O3 content. At the same time, the structures of these films change from the mixture of amorphous and monoclinic phases into high temperature cubic phase. The variations of residual stress correspond to the evolution of structures induced by adding of Y2O3 content.     

Effect of substrate temperature on the magnetic properties and internal stresses of CoPt/AlN multilayer deposited by dc magnetron sputtering

Magnetic properties and internal stresses of AlN(20 nm)/[CoPt(2 nm)/AlN(20 nm)]₅ multilayer structure deposited at different substrate temperatures by dc magnetron sputtering have been studied. It is found that with increasing the substrate temperature from room temperature to 400 °C, in-plane magnetic anisotropy field of the film becomes smaller, and the out-of-plane magnetization becomes stronger. Especially when the film is deposited at substrate temperature of 400 °C, the out-of-plane magnetization becomes as strong as the in-plane magnetization. On the other hand, the total in-plane residual stress of the film changes gradually from compressive to tensile. The compressive intrinsic stress is generated during deposition process and decreases with increasing the substrate temperature. After annealing at high temperatures, the films show strong perpendicular magnetic anisotropy. With increasing the annealing temperature, the in-plane thermal stress also increases and becomes dominant, which is considered to result in the perpendicular magnetic anisotropy of the films.     

Structural and microwave properties of (Ba,Sr)TiO3 films grown by pulsed laser deposition

The relationship between the structure and the microwave dielectric properties of epitaxial Ba_0.5Sr_0.5TiO₃ (BST) films has been investigated. Single-phase BST films (40-160 nm) have been deposited onto (100) MgO substrates by pulsed laser deposition. As-deposited films show a significant tetragonal distortion. The in-plane lattice parameters (a) are always larger than the surface normal lattice parameters (c). The tetragonal distortion depends on the thickness of the films and the post-deposition annealing conditions. Films annealed at 900 °C show less tetragonal distortion than the as-deposited film and the films annealed at higher temperatures. The distortion in the film is due to stress caused by the lattice mismatch and thermal expansion coefficient differences between the film and the substrate. The dielectric constant and its change with dc bias voltage of BST films on MgO at microwave frequencies increase with increasing annealing temperature from 900 °C to 1200 °C, which corresponds to an increase in the tetragonal distortion.     

Layer structure variations of ultra-thin HfO2 films induced by post-deposition annealing

To meet challenges for a smaller transistor feature size, ultra-thin HfO₂ high-k dielectric has been used to replace SiO₂ for the gate dielectric. In order to accurately analyze the ultra-thin HfO₂ films by grazing incidence X-ray reflectivity (GIXRR), an appropriate material model with a proper layer structure is required. However, the accurate model is difficult to obtain, since the interfaces between layers of the ultra-thin HfO₂ films are not easily identified, especially when post-deposition annealing process is applied. In this paper, 3.0 nm HfO₂ films were prepared by atomic layer deposition on p-type silicon wafer, and annealed in Ar environment with temperatures up to 1000 °C. The layer structures and the role of the interfacial layer of the films in the post-deposition annealing processes were evaluated by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The experimental results and analysis showed that layer thicknesses, crystal phases and chemical structures of the ultra-thin HfO₂ films were significantly dependent on annealing temperatures. The binding energy shifts of Hf 4f, O 1s, and Si 2p elements revealed the formation of Hf silicate (Hf-O-Si bonding) with increasing annealing temperatures. Due to the silicate formation and increasing silicon oxide formation, the interface broadening is highly expected. The structure analysis of the GIXRR spectra using the modified material structure model from the XPS analysis confirmed the interfacial broadening induced by the post-deposition annealing.     

Low-temperature growth of epitaxial ZnO films on (001) sapphire by ultraviolet- assisted pulsed laser deposition

ZnO thin films have been grown on thin Si₃N₄ membranes and (001) sapphire substrates by an ultraviolet-assisted pulsed laser deposition (UVPLD) technique. The microstructure of the films grown on Si₃N₄ membranes, investigated by transmission electron microscopy, showed that crystalline and textured films can be grown by UVPLD at a substrate temperature of only 100 °C. For deposition temperatures higher than 400 °C, ZnO films grown on sapphire substrates were found to be epitaxial by Rutherford backscattering (RBS) and X-ray diffraction measurements. The minimum yield of channeling RBS spectra recorded from films deposited at 550 °C was around 2% and the FWHM of the rocking curve for the (002) diffraction peak was 0.17°; these values are similar to those recorded from ZnO layers grown by conventional PLD at 750 °C.     

Si nanocrystallites in SiO2 with intense visible photoluminescence synthesized from SiOx films deposited by laser ablation

We observed very intense and highly reproducible photoluminescence (PL) spectra for SiO_x films obtained by laser ablation of Si targets in 50-mTorr oxygen gas followed by proper annealing. It was found that the PL peak continuously changes from 1.4 eV at the center of the samples to 1.8 eV at the sample edge. The optimum values of the oxygen component in SiO_x was x=1.3-1.4 and the optimum annealing temperature was 1000 °C for intense PL. From transmission electron microscopy images of annealed films, Si nanocrystallites are found to be formed in the matrix of SiO₂ grown from the SiO_x and have diameters of 2-3 nm. These indicate that a high density of Si nanocrystallites with diameters of 2-3 nm in the SiO₂ phase are probably responsible for the PL and that the Si nanostructure is well formed from the as-deposited, metastable SiO_x (x=1.3-1.4) films by annealing at 1000 °C.     

Temperature dependent surface and spectral modifications of nano V<Subscript>2</Subscript>O<Subscript>5</Subscript> films

Nanocrystalline V₂O₅ films have been deposited on glass substrates at 300°C substrate temperature using thermal evaporation technique and were subjected to thermal annealing at different temperatures 350, 400, and 550°C. X-ray diffraction (XRD) spectra exhibit sharper and broader characteristic peaks respectively indicating the rearrangement of nanocrystallite phases with annealing temperatures. Other phases of vanadium oxides started emerging with the rise in annealing temperature and the sample converted completely to VO₂ (B) phase at 550°C annealing. FESEM images showed an increase in crystallite size with 350 and 400°C annealing temperatures followed by a decrease in crystallite size for the sample annealed at 550°C. Transmission spectra showed an initial redshift of the fundamental band edge with 350 and 400°C while a blue shift for the sample annealed at 550°C, which was in agreement with XRD and SEM results. The films exhibited smart window properties as well as nanorod growth at specific annealing temperatures. Apart from showing the PL and defect related peaks, PL studies also supported the observations made in the transmission spectra.     

Effects of Annealing Temperature on Structural and Optical Properties of ZnO Thin Films

The effects of annealing temperature on the structural and optical properties of ZnO films grown on Si （100） substrates by sol-gel spin-coating are investigated. The structural and optical properties are characterized by x-ray diffraction, scanning electron microscopy and photoluminescence spectra. X-ray diffraction analysis shows the crystal quality of ZnO films becomes better after annealing at high temperature. The grain size increases with the temperature increasing. It is found that the tensile stress in the plane of ZnO films first increases and then decreases with the annealing temperature increasing, reaching the maximum value of 1.8 GPa at 700℃. PL spectra of ZnO films annealed at various temperatures consists of a near band edge emission around 380 nm and visible emissions due to the electronic defects, which are related to deep level emissions, such as oxide antisite （OZn）, interstitial oxygen （Oi）, interstitial zinc （Zni） and zinc vacancy （VZn^-）, which are generated during annealing process. The evolution of defects is analyzed by PL spectra based on the energy of the electronic transitions.     

Effects of Annealing on Microstructure and Optical Properties of TiO2 Sculptured Thin Films

The evolution of microstructure and optical properties of TiO2 sculptured thin films under thermal annealing is reported. XRD, field emission SEM, UV-Vis-NIR spectra are employed to characterize the microstructural and optical properties. It is found that the optimum annealing temperature for linear birefringence is 500℃. The maximum of transmission difference for linear birefringence is up to 18%, which is more than twice of that in as-deposited thin films. In addition, the sample annealed at 500℃ has a minimum of column angle about 12℃. The competitive process between the microstructural and optical properties is discussed in detail. Post-annealing is a useful method to improve the linear birefringence in sculptured thin films for practical applications.     

Oxygen Recovery in Hf Oxide Films Fabricated by Sputtering

The chemical structure of ultrathin Hf oxide films （〈 10 nm） fabricated by a standard sputtering method is investigated using x-ray spectroscopy and Rutherford backseattering spectroscopy. According to the experiments, oxygen species are impacted to the HfO2/Si interface during the initial sputtering, and then released back to the upper HfO2 region driven by the oxygen concentration grads. A vacuum annealing can greatly enhance this recovery process. Additionally, significant SiO2 reduction in the interface is observed after the vacuum annealing for the thick HfO2 films in our experiment. It might be an effective method to confine the interracial layer thickness by sputtering thick HfO2 in no-oxygen ambient.     

沉积速率和氧分压对HfO2薄膜残余应力的影响

采用ZYGO MarkIII-GPI数字波面干涉仪对以K9玻璃为基底的电子束蒸发方法制备的HfO₂薄膜中的残余应力进行了研究,讨论了沉积速率、氧分压这两种工艺参量对HfO₂薄膜残余应力的影响.实验结果表明：在所有的工艺条件下,薄膜的残余应力均为张应力;随着沉积速率的升高,氧分压的减小,薄膜的堆积密度逐渐增大,而残余应力呈减小趋势.同时用X射线衍射技术测量分析了不同工艺条件下HfO₂薄膜的晶体结构,探讨了HfO₂薄膜晶体 关键词： 残余应力 2薄膜')" href="#">HfO₂薄膜 沉积速率 氧分压     

A Spectroscopic Ellipsometry Study of TiO2 Thin Films Prepared by dc Reactive Magnetron Sputtering： Annealing Temperature Effect

TiO2 thin films are obtained by dc reactive magnetron sputtering. A target of titanium （99.995%） and a mixture of argon and oxygen gases are used to deposit TiO2 films on to silicon wafers （100）. The crystalline structure of deposited and annealed film are deduced by variable-angle spectroscopic ellipsometry （VASE） and supported by x-ray diffractometry. The optical properties of the films are examined by VASE. Measurements of ellipsometry are performed in the spectral range O. 72-3.55 e V at incident angle 75^o. Several SE models, categorized by physical and optical models, are proposed based on the ＇simpler better＇ rule and curve-fits, which are generated and compared to the experimental data using the regression analysis. It has been found that the triple-layer physical model together with the Cody-Lorentz dispersion model offer the most convincing result. The as-deposited films are found to be inhomogeneous and amorphous, whereas the annealed films present the phase transition to anatase and rutile structures. The refractive index of TiO2 thin films increases with annealing temperature. A more detailed analysis further reveals that thickness of the top sub-layer increases, whereas the region of the bottom amorphous sub-layer shrinks when the films are annealed at 300℃.     

Pulsed laser deposition of tantalum pentoxide film

We report thin tantalum pentoxide (Ta₂O₅) films grown on quartz and silicon substrates by the pulsed laser deposition (PLD) technique employing a Nd:YAG laser (wavelength 5=532 nm) in various O₂ gas environments. The effect of oxygen pressure, substrate temperature, and annealing under UV irradiation using a 172-nm excimer lamp on the properties of the grown films has been studied. The optical properties determined by UV spectrophotometry were also found to be a sensitive function of oxygen pressure in the chamber. At an O₂ pressure of 0.2 mbar and deposition temperatures between 400 and 500 °C, the refractive index of the films was around 2.18 which is very close to the bulk Ta₂O₅ value of 2.2, and an optical transmittance around 90% in the visible region of the spectrum was obtained. X-ray diffraction measurements showed that the as-deposited films were amorphous at temperatures below 500 °C and possessed an orthorhombic (#-Ta₂O₅) crystal structure at temperatures above 600 °C. The most significant result of the present study was that oxygen pressure could be used to control the composition and modulate optical band gap of the films. It was also found that UV annealing can significantly improve the optical and electrical properties of the films deposited at low oxygen pressures (<0.1 mbar).     

The effect of different ambient gases, pressures, and substrate temperatures on TiO2 thin films grown on Si(100) by laser ablation technique

Pure titanium dioxide (TiO₂) thin films were deposited on single-crystal Si(100) substrates by laser ablation. We investigated the effects of ambient gas (O₂ or Ar), pressures, and substrate temperatures on film quality. From the annealing experiment of the deposited TiO₂ thin film under Ar or O₂ ambient gas, we see the chemical effect of ambient gas on film quality. The crystallinity of the deposited TiO₂ thin film is best at 700 °C in the substrate temperature range attempted, 400-700 °C, and at pressures of 0.1 Torr and below. The rutile phase is dominant under most experimental conditions. Only under very extreme conditions did we obtain a thin film of the anatase phase.     

Effects of thermal annealing on titanium oxide films prepared by ion-assisted deposition

Titanium oxide thin films are prepared at a substrate temperature of 250 °C by electron-beam evaporation and ionassisted deposition. The effects of thermal annealing temperatures from 100 to 450 °C on the optical and mechanical properties are studied. The optical and mechanical properties include refractive indices, extinction coefficients, residual stress, surface roughness and crystallization. Experimental results show these properties of titanium oxide films clearly depend on the thermal annealing process.     

Influence of Annealing Temperature on Structure, Optical Loss and Laser-Induced Damage Threshold of TiO2 Thin Films

TiO2 thin films are prepared on fused silica with conventional electron beam evaporation deposition. After annealed at different temperatures for 4h, the spectra and XRD patterns of the TiO2 thin film are obtained. Weak absorption of coatings is measured by the surface thermal lensing technique, and laser-induced damage threshold （LIDT） is determined. It is found that with the increasing annealing temperature, the transmittance of TiO2 films decreases. Especially when coatings are annealed at high temperature over 1173K, the optical loss is very serious. Weak absorption detection indicates that the absorption of coatings decreases firstly and then increases, and the absorption and defects play major roles in the LIDT of TiO2 thin films.     

Effect of crystallization on the reliability of unipolar resistive-switching in HfO2-based dielectrics

The electroforming and unipolar resistive switching characteristics of as-deposited and annealed HfO₂ and Hf_0.6Si_0.4O₂ films are reported. The reliability of HfO₂ devices is shown to be significantly degraded by annealing at 600 °C, during which the film is observed to crystallize. In contrast, the characteristics of Hf_0.6Si_0.4O₂ devices subjected to the same annealing conditions are found to be unchanged, consistent with the fact that the films remain amorphous. These differences are attributed to the presence of grain boundaries and can have important implications for the use of HfO₂ in ReRAM applications.     

Investigation of Oxygen Vacancy and Interstitial Oxygen Defects in ZnO Films by Photoluminescence and X-Ray Photoelectron Spectroscopy

ZnO films prepared at different temperatures and annealed at 900^o C in oxygen are studied by photoluminescence （PL） and x-ray photoelectron spectroscopy （XPS）. It is observed that in the PL of the as-grown films the green luminescence （GL） and the yellow luminescence （YL） are related, and after annealing the GL is restrained and the YL is enhanced. The 0 ls XPS results also show the coexistence of oxygen vacancy （Vo） and interstitial oxygen （Oi） before annealing and the quenching of the Vo after annealing. By combining the two results it is deduced that the GL and YL are related to the Vo and Oi defects, respectively.