Amorphous SiO2 Layer Research Articles

Grain orientation in thick laser-deposited Y1Ba2Cu3O7−δ films: Adjustment of c-axis orientation

Y1Ba2Cu3O7−δ films with a thickness between 0.5 and 5 μm were grown on Si covered with an amorphous SiO2 layer, on Zr foils, and on a single-crystalline MgO substrates by KrF laser ablation. The influence of film thickness and substrate temperature on the structure, texture, and microstructure of the as-grown films was investigated by x-ray diffraction and scanning electron microscopy. At an appropriate, substrate-dependent temperature, on all three substrate materials, the films grow c-axis oriented up to a thickness of about 2 μm (critical thickness), followed by a sharp transition to a-axis-oriented growth occurring within about 100 nm. Similar changes could be observed by lowering the substrate temperature by 120 °C. Therefore, the hypothesis was propounded that the thickness dependence of the growth orientation of the film is due to a decrease of the surface temperature. To prove this the influence of raising the substrate temperature during the growth process was investigated. It could be shown that a linear increase of the substrate temperature leads to completely c-axis-oriented films up to thicknesses of 5 μm. A change of the thermal emissivity of the film surface as a possible cooling mechanism is discussed.

Characterization of Metal/Ferroelectric/Insulator/Semiconductor Structure with CeO2 Buffer Layer

A PbTiO3 ferroelectric film 813 Å thick was grown on a CeO2/Si(100) substrate by the digital chemical vapor deposition method. As the buffer layer between the perovskite PbTiO3 film and Si substrate, a CeO2 intermediate layer was grown on the Si(100) substrate using an ultrahigh vacuum (UHV) system. The density of surface states at the CeO2/Si(100) interface was estimated from the capacitance-vs-voltage (C-V) characteristics of Al/CeO2/Si(100) samples to be 8×1011/cm2 eV, and CeO2 films on Si(100) are therefore expected to be suitable as gate oxides for metal/ferroelectric/semiconductor-field-effect transistors (FETs). Experimental results derived from the C-V characteristics of metal/ferroelectric/insulator/semiconductor (MFIS)-structured samples show that the MFIS structure has ferroelectric switching properties, as demonstrated by the roughly 2.4 V threshold hysteresis in its C-V characteristics (“memory window”). Furthermore, the retention time of the MFIS sample was estimated to be 100,000 s by measuring the time dependence of capacitance at the voltage at the centuer of the memory window. Interfacial lines of the MFIS structure were clear in a transmission electron microscope image, and an amorphous CeOx layer and an amorphous SiO2 layer were seen between the Si substrate and PbTiO3 film. Secondary ion mass spectroscopy revealed that there was little diffusion of Si atoms into the PbTiO3 layer on the CeO2/Si substrate.

Y–Ba–Cu–O multilayer structures with amorphous dielectric layers for multichip modules using ion-assisted pulsed-laser deposition

Existing technology to construct high-temperature superconductor (HTSC) multichip modules (MCM’s) incorporating several YBa2Cu3O7−δ (YBCO) thin films and thick dielectric layers are based on epitaxial growth of all layers from the template of a single-crystal substrate. This work demonstrates an alternate method to fabricate these structures: the use of a biaxially aligned yttria-stabilized zirconia (YSZ) intermediate layer deposited by ion-assisted pulsed-laser deposition. Using this technique, a YBCO thin film with Tc∼87 K and Jc∼3×105 A/cm2 was grown on a 5 μm amorphous SiO2 layer. In addition, YBCO/YSZ/SiO2/YSZ/YBCO/CeO2/YSZ and YBCO/YSZ/amorphous-YSZ/YBCO/CeO2/YBCO multilayer structures were constructed.

In situ real time measurement of the incubation time for silicon nucleation on silicon dioxide in a rapid thermal process

Real time ellipsometry and atomic force microscopy (AFM) were used to measure critical nucleation parameters for polycrystalline silicon deposition on an amorphous SiO2 layer by rapid thermal chemical vapor deposition (RTCVD) using disilane (5% in helium). A particularly important parameter for selective epitaxial deposition is the time for nuclei to form, the incubation time. Quantitation of the nucleation parameters, such as the nuclei density, nuclei growth rate, nuclei coalescence, and an operational incubation time were determined from the real time ellipsometric measurements and confirmed by AFM. For a substrate temperature of 700 °C and at a chamber pressure of 0.2 Torr, the nuclei densities of 1.4×1010 nuclei/cm2, incubation time of 26 s and nuclei layer growth rates of 20 nm/min were obtained.

Growth of Crystalline SrTiO3 Films on Si Substrates Using Thin Fluoride Buffer Layers and Their Electrical Properties

Strontium titanate ( SrTiO3: STO) films were grown epitaxially on Si (111) and (100) substrates using thin SrF2 buffer layers. The SrF2 buffer layer was used for preventing the formation of an amorphous SiO2 layer on the Si substrate during deposition of an STO film. It was found from X-ray diffraction (XRD) analysis that well (110)-oriented STO films were grown on Si(111) substrates by a two-step growth method, in which a thin (8 nm thick) STO film was predeposited on the SrF2 buffer layer at 450°C and a thick (80 nm thick) STO film was successively deposited at 750°C. It was also found from XRD and Auger electron spectroscopy (AES) measurements that the SrF2 buffer layer was completely dissolved during STO film deposition at 750°C, and no fluorine (F) atoms existed in the buffer layer. The epitaxial relationship on Si(111) substrates revealed by X-ray pole figure measurements was (110)STO//(111)Si and <110>STO//<112>Si, while that on Si(100) substrates was (100)STO//(100)Si and <110>STO//<110>Si or <110>STO//<100>Si. Concerning the electrical properties of STO films, the best values of breakdown field (at 1 µ A/cm2), resistivity (at 1 MV/cm), and relative dielectric constant were 2.3 MV/cm, 8.2×1012 Ω· cm and 72, respectively.

Epitaxial Relationships and Electrical Properties of SrTiO3 Films on Various Thin -Fluoride/Si Structures

AbstractCrystalline strontium titanate (SrTiO3:STO) films were grown on Si(111) and Si(100) substrates using thin SrF2 and CaF2 buffer layers by two-step growth method. In all cases, fluoride buffer layers were effective in growing STO films on Si substrates, which is probably due to that fluoride buffer layers have excellent crystallinity and they can prevent formation of amorphous SiO2 layers on Si substrates at the initial stage of the STO deposition. It was found from X-ray diffraction and pole-figure measurements that (110)-oriented STO crystallites with three different positions to the substrate were grown on Si(111) substrates for both SrF2 and CaF2 buffer layers. In constrast, (100)-oriented STO films with 12-fold symmetry were grown on a SrF2/Si(100), and mixed (110)- and (100)-oriented STO crystallites were grown on a CaF2/Si(100) structure. It was concluded from these results that better crystallinity of STO films can be obtained on the SrF2 buffer layer in case of Si(111) and on the CaF2 buffer layer in case of Si(100). It was also found from I-V and C-V analyses that the STO films have good insulating and dielectric characteristics. For a SrTiO3 film on SrF2/Si(111) structure, the best values of breakdown field (at l.μA/cm2), resistivity (at IMV/cm) and dielectric constant were 2.3MV/cm, 8.2 × 1012 Ωcm and 72, respectively.

Microstructure of interfaces between a magnesium matrix and preoxidized silicon carbide particles

An amorphous SiO2 layer, 100–150 nm thick, has been produced on the surface of α-SiC particles by controlled oxidation in air. The as-treated particles were immersed for 1.5h at 1,000 K in a large excess of liquid magnesium, which resulted in the formation by pressureless infiltration of a composite region with a particle volume fraction about 50%. Conventional transmission electron microscopy (CTEM) and high-resolution TEM (HRTEM) were used to characterize and localize the different species present in the transition zone between the Mg matrix and the α-SiC particles. The results are discussed in terms of the physico-chemical processes occurring during formation of the composite region or during cooling of the Mg ingot. A reaction mechanism based on local equilibria and liquid phase diffusion is proposed. Four steps are involved in this mechanism: (i) rapid conversion of SiO2 into MgO and Si; (ii) formation of a true Mg/SiC interface; (iii) partial decomposition of SiC into carbon and silicon; and (iiii) precipitation of β-SiC and Mg2Si on cooling.

Formation of metallic, crystalline NiSi2 thin film on amorphous SiO2/Si

Thin metallic, oriented crystalline NiSi2 films that are suitable for additional epitaxial growth have been formed on amorphous SiO2 layers on Si substrates. The orientation of the Si substrate is maintained in the NiSi2 film as if the SiO2 is not present. This was achieved by combining the separation by implantation of oxygen process and e-beam evaporation techniques. The results are comparable with NiSi2 films formed directly on Si. This technique should, in general, be applicable to other silicides that have been epitaxially grown on Si.

Orientation relationships of epitaxial oxide buffer layers on silicon (100) for high-temperature superconducting YBa2Cu3O7−x films

The preparation parameters of epitaxially grown buffer layers on silicon (100) wafers were investigated. We found that an in situ removal of the native amorphous SiO2 layer from the Si surface is possible, avoiding the etching of the wafer prior to the deposition. YSZ and Y2O3 were chosen as buffer layers for subsequent YBa2Cu3O7−x thin-film deposition. The orientation of the thin films during the deposition process was analyzed by RHEED. Different orientations on the substrates are obtained depending on the evaporation parameters. TEM studies of the interfaces, x-ray diffraction analysis, and measurements of the superconducting properties were made after the deposition of the films.

A New Model Variant for Describing Dielectric Response on the Basis of the Impact of Low‐Energy Excitations

AbstractThe anomalous behaviour of very different physical characteristics in vitreous solids, particularly their dielectric behaviour, can be described by a system of additional low‐energy excitations. This holds also for the amorphous SiO2 layers in MOS structures. Therefore, an available model of time‐dependent dielectric response is completed. This model represents the basis for further research, especially of the dielectric behaviour of vitreous solids.

A model for describing dielectric breakdown in vitreous solids based on the concept of low‐energy excitations

AbstractThe anomalous behaviour of different physical characteristics in vitreous solids compared to the behaviour in the crystalline phase, in particular their dielectric behaviour, can be described by the concept of a system of low‐energy excitations in these solids. This concept is also applicable for amorphous SiO2 layers in MOS structures. Thus, a model of breakdown behaviour based on the assumption of the existence of fluctuations of correlated local internal electrical fields and low‐energy excitations within these layers is elaborated.

Computed tomography for quantitative NDE: 37610 Streit, R.D.; Clark, G.A.; Brase, J.M. Mechanical Engineering, Vol. 109, No. 9, pp. 56–64 (Sep. 1987)

The results of X-ray photoelectron spectra (XPS valence band and core levels) measurements for Ge+ implanted SiO2/Si heterostructures are presented. These heterostructures have a 30 nm thick Ge+ ion implanted amorphous SiO2 layer on p-type Si. The chemical-state transformation of the host-matrix composition after Ge+ ion implantation and rapid thermal annealing (RTA) are discussed. The XPS-analysis performed allows to conclude the formation of Ge0 and GeOx clusters within the samples under study. It was established, that the annealing time strongly affects the degree of oxidation states of Ge-atoms.

Oxidation Kinetics Of Mosi2 And Mosi2/Reinforcement Mixtures

ABSTRACTAn oxidation study of pure, dense MoSi 2 at 400-600°C and MoSi2/20 vol. % (TiB2, Al2O3, Nb) mixtures at 400–1200°C has been performed. Dense MoSi2 does not fail catastrophically (“pest”) in dry air, wet air, or oxygen, and oxidizes heavily only near 500°C. Heavy oxidation is related to the slow growth of a protective, amorphous SiO2 layer; a low rate of Mo removal as vapor species; and cracking of an initially protective Mo9O26-SiO2 layer. Pre-oxidation of MoSi2 at 1200°C prevents subsequent heavy oxidation at 500°C. MoSi2/TiB2 and MoSi2/A12O3 mixtures oxidize more slowly than MoSi2 for T &lt; 600°C and more rapidly for T &gt; 600°C. Protective oxides are formed on MoSi2/reinforcement mixtures except at 500°C, for which high-temperature pre-oxidation is again effective. MoSi2/Nb mixtures suffer severe mass losses upon oxidation at both 500 and 1200°C owing to rapid oxidation of the Nb and spalling of the product Nb2O5 Only the latter case poses problems for the application of MoSi2-matrix composites as high-temperature materials.

Healing layer formation in Fe–Cr–Si ferritic steels

The addition of small amounts of Si can dramatically improve the oxidation resistance of Fe and Fe–Cr steels. It is found that steels with Si contents above a certain critical value oxidise at a much slower rate and also become virtually immune to breakaway oxidation in high pressure CO2, The critical Si content for this behaviour is found to vary with the Cr content (wt-%) of the steel, from about 2·5% for mild steel to 0·7% for 9%Cr steel to 0·3% for 11%Cr steel in the temperature range 575–650°C. The lower Si content required for Cr steels than for mild steels is advantageous, because it is small enough not to degrade the other metallurgical properties such as creep strength. The beneficial effect of Si is thought to arise from the formation of a near continuous ‘healing’ layer of amorphous SiO2 at the oxide/metal interface which acts as a diffusion barrier to further transport of metal ions to the scale. The conditions required for the development of such layers are analysed using standard models of selective oxidation. The synergistic effect of Cr and Si is ascribed to the action of Cr as a secondary getter, in which it reduces the oxygen solubility in the metal and so reduces the Si content required to form a healing layer. Chromium also discourages the SiO2 from converting to fayalite (Fe2SiO4) which is a much poorer diffusion barrier. The conventional theory of selective oxidation and secondary gettering is found to describe reasonably well the compositional limits of healing layer behaviour in these ferritic steels. However, the silica also seems to encourage the formation of a chromia based layer at the base of the overlying oxide and the oxidation rate during healing seems to be limited eventually by this chromia layer rather than the silica layer, as would be expected in the conventional model.MST/1074

ChemInform Abstract: Anodic Oxidation of Hydrogenated Amorphous Silicon and Properties of Oxide.

AbstractIt is shown that uniform amorphous SiO2 layers of up to 2500 Å thickness can be grown on hydrogenated amorphous silicon (a‐Si:H) at room temp. by anodic oxidation in an ethylene glycol solution of KNO3 at a rate of 5.5 Å/V. The process is stable, reproducible, and electrically controllable.

The influence of silicon on the high-temperature oxidation of nickel

An investigation of the oxidation of nickel-silicon alloys has been carried out in order to ascertain the mode of development of partially or fully protective SiO2 layers. The addition of 1% Si has little effect on the oxidation rate of nickel at 1000°C but is sufficient for partial-healing layers of amorphous SiO2 to be established. These layers are incorporated into the inner part of the duplex NiO scale but do not react with the oxide to form a double oxide. Increasing the silicon concentration to 4% or 7% facilitates the development of apparently continuous amorphous SiO2 layers at the base of the NiO scale, resulting in reduced rates of oxidation. However, these layers develop imperfections, possibly microcracks resulting from oxide growth stresses, and are unable to prevent some continued transport of Ni2+ ions into the NiO scale and oxygen into the alloy, particularly for Ni-4% Si. Although the formation of SiO2-healing layers can reduce the rate of oxidation of nickel, they provide planes of weakness that result in considerable damage under the differential thermal contraction stresses during cooling. In particular, severe scale spalling occurs for Ni-4% Si and Ni-7% Si as failure occurs coherently within the SiO2 layer.

Vibrational study of the SiO2/Si interface by high resolution electron energy loss spectroscopy

By using high resolution electron energy loss spectroscopy (HREELS) the surface phonon spectra of SiO2(0001) and of thick amorphous SiO2 layers have been measured. The spectra recorded on the crystalline surface are characterized by three first order peaks at 498, 798, and 1176 cm−1. The HREELS data could be interpreted by the dielectric theory applied to anisotropic material, and the optical constants were compared to infrared spectroscopy values. HREELS spectra as a function of oxide thickness could be obtained from oxidized Si(100) wafers by sputter erosion. Peak positions shifted to lower frequencies and intensities decreased regularly with decreasing oxide thickness. At the interface a transition layer of about 25 Å was observed and carbon contamination was identified. The dielectric theory applied to a thin homogeneous supported film cannot account for the observed frequency shift.

Energy loss of warm electrons at the interface of (100) silicon MOSFETs

The electrons in inversion layers of (100) silicon MOSFETs were heated at helium temperatures with source drain fields of the order l Vcm. The electron temperature as derived from the amplitudes of Shubnikov-De Haas oscillations was studied as a function of lattice temperature and substrate bias Usb. Whereas at temperatures of about 4 K. the electron temperature hardly changed with substrate bias, it increased substantially with Usb, at temperatures of 2 K and lower. This observation cannot he explained by currently discussed models for the electron energy losses. It is proposed that the low temperature behaviour arises from the anomalous thermal and dielectric properties of the amorphous SiO2 layer adjacent to the channel. Various experiments indicate that vitreous SiO2 can be considered as a two-level system with low energy excitations.

ENERGY LOSS OF WARM ELECTRONS AT THE INTERFACE OF (100) SILICON MOSFETs

The electrons in inversion layers of (100) silicon MOSFETs were heated at helium temperatures with source drain fields of the order 1 V/cm. The electron temperature as derived from the amplitudes of Shubnikov-de Haas oscillations was studied as a function of lattice temperature and substrate bias Usb. Whereas at temperatures of about 4 K the electron temperature hardly changed with substrate bias, it increased substantially with Usb at temperatures of 2 K and lower. This observation cannot be explained by currently discussed models for the electron energy losses. It i s proposed that the low temperature behaviour arises from the anomalous thermal- and dielectric properties of the amorphous SiO2 layer adjacent to the channel. Various experiments indicate that vitreous SiO2 can be considered as a twolevel system with low energy excitations.

Scattering loss reduction in ZnO optical waveguides by laser annealing

We report successful laser annealing of ZnO optical waveguides deposited on an amorphous SiO2 layer thermally grown on Si. A significant improvement in the optical attenuation of the fundamental mode from several dB/cm before laser annealing to as low as 0.01 dB/cm after laser annealing is observed. Scattering loss measurements for the m = 1 and m = 2 mode are also reported. We attribute the reduction in loss primarily to an improvement in the quality of the ZnO film in the region near the ZnO-SiO2 interface.