SiOx films prepared using RF magnetron sputtering with a SiO target

In this study, SiO_x thin films were prepared using reactive radio frequency magnetron sputtering at room temperature with a SiO sintered target. The obtained SiO_x films were identified using X-ray diffraction, transmission electron microscopy, infrared absorption spectroscopy, X-ray photoelectron spectroscopy and ultraviolet-visible transmittance measurement. The x in SiO_x film was controlled from 0.98 to 1.70 by changing the oxygen flow ratio at deposition. Increasing the oxygen flow ratio increased the optical gap of the SiO_x films from 3.7 to greater than 6 eV.     

Mesoporous materials from SiO2 and NiTiO3

In this work, we synthesized and characterized mesoporous thin films of SiO₂ and NiTiO₃ structured by a surfactant called Brij58. These films were fabricated by the method of dip coating and the best conditions for well-structured thin films were investigated as a function of surfactant concentration and different types of substrates. These films have been characterized by X-ray reflectivity which was calculated using the matrix formalism. We demonstrated that the silicon substrate had a great effect on the structure and porosity of the fabricated films for both SiO₂ and NiTiO₃. Furthermore, we found that mesoporosity has been increased as a function of the surfactant concentration in the solution. This experimental procedure allows also to produce NiTiO₃ powders which have been characterized by X-ray diffraction. The XRD coupled to the crystallographic software “Maud”shows that the samples are constituted by 98, 2% NiTiO₃ powders.     

Characterisation of ALCVD Al2O3-ZrO2 nanolaminates, link between electrical and structural properties

Al₂O₃ and ZrO₂ mixtures for gate dielectrics have been investigated as replacements for silicon dioxide aiming to reduce the gate leakage current and reliability in future CMOS devices. Al₂O₃ and ZrO₂ films were deposited by atomic layer chemical vapor deposition (ALCVD) on HF dipped silicon wafers. The growth behavior has been characterized structurally and electrically. ALCVD growth of ZrO₂ on a hydrogen terminated silicon surface yields films with deteriorated electrical properties due to the uncontrolled formation of interfacial oxide while decent interfaces are obtained in the case of Al₂O₃. Another concern with respect to reliability aspects is the relatively low crystallization temperature of amorphous high-k materials deposited by ALCVD. In order to maintain the amorphous structure at high temperatures needed for dopant activation in the source drain regions of CMOS devices, binary Al/Zr compounds and laminated stacks of thin Al₂O₃ and ZrO₂ films were deposited. X-ray diffraction and transmission electron microscope analysis show that the crystallization temperature can be increased dramatically by using a mixed oxide approach. Electrical characterization shows orders of leakage current reduction at 1.1-1.7 nm of equivalent oxide thickness. The permittivity of the deposited films is determined by combining quantum mechanically corrected capacitance voltage measurements with structural analysis by transmission electron microscope, X-ray reflectivity, Rutherford backscattering, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectroscopy. The k-values are discussed with respect to formation of interfacial oxide and possible silicate formation.     

Effect of oxygen content on barrier properties of silicon oxide thin film deposited by dual ion-beam sputtering

A silicon oxide thin film barrier was prepared with various oxygen contents and its chemical composition, surface morphology and optical and barrier properties were related to the deposition conditions used. Our study showed that under Ar and O₂ assisted process conditions, a stoichiometric silicon oxide thin film formed at a critical oxygen content during deposition of 40-50%. The thin films deposited at the critical condition showed the lowest surface roughness giving similar or higher optical transmittance than that of the bare polycarbonate (PC) substrate. The boiling and tensile strength test performed on the thin film deposited with assisted ions before the deposition process showed improvement in the adhesion between the oxide layer and the polymer substrate. In addition, interface modification to improve for improving the barrier layer properties of the silicon oxide thin film was achieved through the introduction of dual ion beam sputtering without pre-treatment.     

Thermally oxidized zirconium nanostructured films grown on Si substrates

Zirconium thin films grown on Si substrates by a planar magnetron sputtering system were thermally oxidized at oxygen ambient within 523‐823 K resulting in zirconium oxide films with various stoichiometries. XRD analysis of the ex situ oxidized films revealed the phases at different oxidation temperatures. To achieve a reasonable fit between the experimental and SIMNRA simulated RBS spectra of the prepared samples; it was required to introduce a SiO₂buffer layer in the simulated target between Si substrate and ZrO₂ film. The presence of this intermediate SiO₂ layer was confirmed by observation of SiO₂ phase in the XRD patterns of all the thermally oxidized samples. Using RBS analysis data, the effect of oxidation temperature on the stoichiometry of zirconium oxide films and thickness of ZrO_xand SiO₂ films were investigated. XRD patterns of thermally oxidized Zr films also revealed that crystallization of zirconium oxide films was initiated at about 673 K and was almost completed at 823 K. Diffusion of oxygen atoms through surface layer was investigated and the effective activation energy for oxygen mass transport was estimated to be 1.75 eV using RBS data and Arrhenius relation. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and optical properties of thin films prepared from surface modified ZrO2

This paper describes the preparation and characterization of ZrO₂ thin films deposited on silicon wafer by spin coating method. Nanocrystalline ZrO₂ was synthesized by hydrothermal method using zirconium (IV)-n-propoxide as a precursor material. Surface of the ZrO₂ particles was then modified with 2-acetoacetoxyethyl methacrylate used as a copolymer for coatings. The optical properties, nanostructure and surface morphology of the thin films prepared from surface modified ZrO₂ nanoparticles were examined by optical spectroscopy, X-ray diffraction and scanning electron microscopy, respectively. It was found that the films deposited on silicon wafer have crystalline structure of monoclinic (111) at temperature of 150 °C. It was observed that films depict very dense material that does not present any granular or columnar structure. It was found that optical transparency of thin ZrO₂ films distributed in the range of 30-40 percent in the spectral range 400-800 nm. Refractive index of ZrO₂ films were determined as functions of ZrO₂ content and it was found that the refractive index increases from 1.547 to 1.643 with increased ZrO₂ content.     

Noncrystalline silicon dioxide films on silicon: A review

Firstly, the importance of noncrystalline SiO₂ film in the manufacture of semiconductor devices and integrated circuits is pointed out. After some general remarks on the SiSiO₂ interface, various methods of preparing SiO₂ films on silicon are discussed with emphasis on thermal oxidation of silicon. The transport processes are compared with those occurring in fused silica. Then, the properties of the SiSiO₂ interface structure are summarized; a properly prepared interface is very perfect. This is due to the structural flexibility of noncrystalline SiO₂. Finally, the structural aspects of noncrystalline SiO₂ are discussed on the basis of the chemistry of the SiO bond in which the π component plays a special role. The high degree of short-range order is responsible for many excellent properties of the oxide film. Disruption of the short-range order results in network defects and development of some degree of local order along a direction which it is assumed to give rise to channels. These defects are unique to topologically disordered solids. In this and many other respects, noncrystalline SiO₂ is more similar to siloxane polymers than typical ionic or covalent crystals.     

Preparation of indium tin oxide thin films without external heating for application in solar cells

Indium tin oxide (ITO) films were grown without external heating in an ambient of pure argon by RF-magnetron sputtering method. The influence of argon ambient pressure on the electro-optical properties of as-deposited ITO films was investigated. The morphology, structural and optical properties of ITO films were examined and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and UV–VIS transmission spectroscopy. The deposited ITO films with a thickness of 300 nm show a high transparency between 80% and 90% in the visible spectrum and 14–120 Ω/□ sheet resistance under different conditions. The ITO films deposited in the optimum argon ambient pressure were used as transparent electrical contacts for thin film Cu(In,Ga)Se₂ (CIGS) solar cells. CIGS solar cells with efficiencies of the order of 7.0% were produced without antireflective films. The results have demonstrated that the developed ITO deposition technology has potential applications in thin film solar cells.     

Growth of heavy ion-induced nanodots at the SiO2–Si interface: Correlation with ultrathin gate oxide reliability

Scaling-down the oxide thickness induces weakness influencing its intrinsic reliability. Even unbiased, swift heavy ions irradiated devices clearly show oxide alteration. Despite numerous studies on oxide reliability, some results are not yet well understood. In this paper, we focus on the structural degradation induced in thin silicon oxide films on silicon substrate after a 210 MeV low fluence gold ion irradiation and on its effect on the reliability of MOS devices in radiation-harsh environments. We describe such degradation as a local silicon growth in the SiO₂ layer, near the SiO₂–Si interface. Experimental results can bring some emergent elements to explain earlier works in the field of oxide reliability. Based on the specific behavior of heavy ion-irradiated oxides, this paper aims to link together thermal spike model, heavy ion-induced nanodots and reliability of ultrathin gate oxides. We propose to evaluate the possible sensitivity of some high-k materials in radiation-harsh environments with respect to their thermal conductivity property.     

Study of the nucleation and growth of TiO2 and ZnO thin films by means of molecular dynamics simulations

The nucleation and growth of titanium dioxide (TiO₂) and zinc oxide (ZnO) thin films on Fe₂O₃ (hematite), Al₂O₃ (α-alumina) and SiO₂ (α-quartz) are studied by molecular dynamics simulations. The results show the formation of a strong interface region between the substrate and the film in the six systems studied here. A combination of polycrystalline and amorphous phases are observed in the TiO₂ films grown on the three substrates. ZnO deposition on the Fe₂O₃ and Al₂O₃ crystals yields a monocrystalline film growth. The ZnO film deposited on the SiO₂ crystal exhibits less crystallinity. The simulation results are compared with experimental results available in the literature.     

Growth and characterization of zirconium oxide thin films on silicon substrate

The growth and characterization of zirconium oxide (ZrO₂) thin films prepared by thermal oxidation of a deposited Zr metal layer on SiO₂/Si were investigated. Uniform ZrO₂ thin film with smooth surface morphology was obtained. The thermal ZrO₂ films showed a polycrystalline structure. The dielectric constant of the ZrO₂ film has been shown to be 23, and the equivalent oxide thickness (EOT) of the ZrO₂ stacked oxide is in the range of 3.38–5.43 nm. MOS capacitors with ZrO₂ dielectric stack show extremely low leakage current density, less than 10^?6 A/cm² at ?4 V. Consequently, using this method, high-quality ZrO₂ films could be fabricated at oxidation temperature as low as 600 °C.     

The photochemical metal organic deposition of manganese oxide films from films of manganese(II) 2-ethylhexanoate: a mechanistic study

The photochemistry of thin films of manganese(II) 2-ethylhexanoate to produce manganese oxide films is presented. Thin films of manganese(II) 2-ethylhexanoate can be cast onto silicon wafers by spin coating. The FTIR spectroscopy of these films suggests they exist as chains or clusters with the manganese(II) centers linked by bridging 2-ethylhexanoate ligands. The initial photochemical reaction results in the loss of the bridging 2-ethylhexanoate ligands and the formation of monomeric manganese(II) 2-ethylhexanoate. In this process approximately 60% of the bridging 2-ethylhexanoate ligand is converted to chelating 2-ethylhexanoate while the other 40% fragments to form CO₂, heptane and heptene. Further photolysis resulted in the conversion of the remaining 2-ethylhexanoate ligand to form CO₂, heptane and heptene. The film consisted of manganese(II) oxide although the surface of the film was more oxidized and had carbon impurity on it. Annealing the film resulted in the conversion to polycrystalline α-Mn₂O₃.     

Electrical properties of Bi3.15Nd0.85Ti2.8-xZr0.2MnxO12 thin films with different Mn content synthesized by chemical solution deposition (CSD)

Bi_3.15Nd_0.85Ti_2.8-xZr_0.2Mn_xO₁₂ (BNTZM) thin films with various Mn content (x = 0, 0.005, 0.01, 0.03, and 0.05) have been prepared on Pt/Ti/SiO₂/Si (100) substrates by a chemical solution deposition (CSD) technique. The crystal structures of BNTZM thin film have been analyzed by X-ray diffraction (XRD). The dependence of Mn contents on the ferroelectric, dielectric properties, and leakage current of these BNTZM films have been thoroughly investigated. The XRD analysis demonstrated that all the BNTZM thin films were of typical bismuth-layer-structured ferroelectrics (BLSF) polycrystalline structure and exhibited a highly preferred (117) orientation. Among these BNTZM films, the BNTZM thin film with Mn content equal to 0.01 exhibits the maximum remnant polarization (2P_r) of 48μC/cm² and a low coercive field (2E_c) of 177 kV/cm. In addition, the BNTZM thin film with x = 0.01 (Mn) showed a fatigue-free behavior up to 1 × 10¹⁰ read/write cycles.     

Effects of oxide buffer layers on the microstructure and electrical properties of PLZST 2/87/10/3 antiferroelectric thin films

In the present work, the effects of oxide buffer layers, such as ZrO₂, CeO₂ and TiO₂, on the microstructure and electrical properties of (Pb_0.97La_0.02)(Zr_0.87Sn_0.10Ti_0.03)O₃ (PLZST 2/87/10/3) antiferroelectric (AFE) thin films were investigated systematically. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) pictures illustrated that the crystalline orientation and surface microstructure of PLZST 2/87/10/3 AFE thin films had a close relation with these oxide buffer layers. As a result, the final electrical properties of AFE films were tuned by these buffer layers. Electrical measurements result showed that the dielectric properties, polarization characteristic and current–field curves of AFE thin films could be tailored by selecting a proper oxide buffer layer.     

Electron microscopic study on nucleation and growth of silver particles in a thin glass film

Nucleation and crystal growth of silver particles in a thin glass film of Li₂O·2.6SiO₂ glass containing 0.1 wt% of Ag₂O were observed by transmission electron microscopy and studied by an electron diffraction technique. Anomalies of the image contrast which appeared in the heat-treated specimens were explained to be caused by phase separation of the glass. Nucleation of silver particles was found to occur on the surface of the phase-separated silica-rich droplets. As the silver particles grew, their shape changed into that of a regular cube which was covered with a thin diffusion layer of silver ions about 50 Å in thickness. The presence of this thin layer and the cubic shape suggest that the growth of silver particles proceeds by a layer-by-layer growth mechanism.     

Optical properties and synthesis of CuInSe2 thin films by selenization of Cu/In layers

In this paper, we report the effect of annealing temperature on the properties of copper indium diselenide (CuInSe₂) thin films. The CuInSe₂ thin films were fabricated at 500 °C for 2 h by annealing Cu‐In layers (as precursors) selenized in a glass tube with pure selenium powder. The structural and morphological properties of the CuInSe₂ thin films were characterized respectively by means of x‐ray diffraction (XRD) and field‐emission scanning electron microscope (FE‐SEM). The type of CuInSe₂ thin film has been identified as direct allowed and the band gap value was determined. The study of UV/Visible/NIR absorption shows that the band gap value of CuInSe₂ thin film is about 1.07 eV, which is within an optimal range for harvesting solar radiation energy. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ablation and compaction of amorphous SiO2 irradiated with ArF excimer laser

The structure of amorphous SiO₂ exposed to ArF excimer laser irradiation was examined. Threshold fluence for causing ablation with a single pulse depended on sample preparation: more specifically, 1 J/cm² for thermally grown SiO₂ films on silicon and 2.5 J/cm² for bulk SiO₂. It was found that the bond angle of Si-O-Si was reduced by irradiation near the interface of thermally grown SiO₂ films. In contrast, evolution of the bond angle by irradiation was absent in both the bulk SiO₂ and SiO₂ film-near the top surface, even though the concentration of puckered four-membered rings deduced from Raman spectra dramatically increased. It is assumed that planar three-membered rings were generated in the SiO₂ thin layer near the interface, and puckered four-membered rings were generated in the bulk SiO₂. The concentration of both the Si³⁺ and Si²⁺ structure was increased at a fluence of 800 mJ/cm² with an increasing number of pulses, although generation of both was absent at higher fluence for a single pulse. The author proposes that the structure of SiO₂ is created by flash heating and quenching by pulse laser irradiation. Structural similarities were found between the irradiated SiO₂ and SiO₂ at high temperatures.     

Plasma enhanced chemical vapor deposition of ZnO thin films

Zinc oxide thin films were deposited on silicon and corning-7059 glass substrates by plasma enhanced chemical vapor deposition at different substrate temperatures ranging from 36 to 400 °C and with different gas flow rates. Diethylzinc as the source precursor, H₂O as oxidizer and argon as carrier gas were used for the preparation of ZnO films. Structural and optical properties of these films were investigated using X-ray diffraction, reflection high energy electron diffraction, atomic force microscopy and photoluminescence. Highly oriented films with (0 0 2) preferred planes were obtained on silicon kept at 300 °C with 50 ml/min flow rate of diethylzinc without any post annealing. Reflection high energy electron diffraction pattern also showed the crystalline nature of these films. A textured surface with rms roughness ∼28 nm was observed by atomic force microscopy for the films deposited at 300 °C. A sharp peak at 380 nm in the PL spectra indicated the UV band-edge emission.     

Effects of the Substrate Crystals upon the Structure of Thermal Oxide Layers on Si

Comparisons of Bragg reflections from thermal oxide thin films on Si wafers were made for five sets of samples with various kinds of substrates. The intensities of the reflections for the samples with the substrate of better quality were stronger than those of poor one, indicating that the structures of the crystalline SiO₂ in the oxide layer were related with the quality of the Si substrates. It is also shown that no diffraction peaks were observed from the oxide layers grown on Si substrates by chemical vapor deposition.