Structure and thermal stability of MOCVD ZrO2 films on Si (1 0 0)

The structure and thermal stability of ZrO₂ films grown on Si (1 0 0) substrates by metalorganic chemical vapor deposition have been studied by high-resolution transmission electron microscopy, selected area electron diffraction and X-ray energy dispersive spectroscopy. As-deposited films consist of tetragonal ZrO₂ nanocrystallites and an amorphous Zr silicate interfacial layer. After annealing at 850°C, some monoclinic phase is formed, and the grain size is increased. Annealing a 6 nm thick film at 850°C in O₂ revealed that the growth of the interfacial layer is at the expense of the ZrO₂ layer. In a 3.0 nm thick Zr silicate interfacial layer, there is a 0.9 nm Zr-free SiO₂ region right above the Si substrate. These observations suggest that oxygen reacted with the Si substrate to grow SiO₂, and SiO₂ reacted with ZrO₂ to form a Zr silicate interfacial layer during the deposition and annealing. Oxygen diffusion through the tetragonal ZrO₂ phase was found to be relatively easier than through the monoclinic phase.     

Toughened glass-ceramics containing ZrO2 and Al2O3 prepared by the sol-gel process from metal alkoxides

Glasses of compositions 5ZrO₂·5SiO₂(ZS), 5ZrO₂·Al₂O₃·4SiO₂(ZAS) and 5 5ZrO₂·0.5Al₂O₃·0.5Na₂O·4SiO₂(ZANS) were prepared by the sol-gel process from metal alkoxides and sintered to make glass-ceramics. Tetragonal ZrO₂ was precipitated by heat treatment at 900 to 1300°C. The activation energy for tetragonal ZrO₂ crystal growth was extremely high in Al₂O₃ containing glasses. ZAS and ZS were sintered to the near theoretical densities above 1200°C, at which the predominant phase was tetragonal ZrO₂. On the other hand, for ZANS, high densification was not attained owing to the large pores enclosed by the glass phase. Strength and fracture toughness increased with the densification and the crystal growth of tetragonal ZrO₂, reaching 450 MPa and 9 MN/m^1.5, respectively.     

Rotary target method to prepare thin films of CdS/SiO2 by pulsed laser deposition

Thin films of CdS-doped SiO₂ glass were prepared by using the conventional pulsed laser deposition (PLD) technique. The laser target consisted of a specially constructed rotary wheel which provided easy control of the exposure-area ratio to expose alternately the two materials to the laser beam. The physical target assembly avoided the potential complications inherent in chemically mixed targets such as in the sol–gel method. Time-of-flight (TOF) spectra confirmed the existence of the SiO₂ and CdS components in the thin-film samples so produced. X-ray diffraction (XRD) and atomic force microscopy(AFM) results showed the different sizes and structures of the as-deposited and annealed films. The wurtzite phase of CdS was found in the 600^oC-annealed sample, while the as-deposited film showed a cubic–hexagonal mixed structure. In the corresponding PL (photoluminescence) spectra, a red shift of the CdS band edge emission was found, which may be a result of the interaction between the CdS nanocrystallite and SiO₂ at their interface.     

Solidification of superalloy in a SiO2–ZrO2–B2O3 coating mould

The preparation of glass-lined coating mould from gels in the ternary system of SiO₂–ZrO₂–B₂O₃ has been investigated. The crystallization characterization and high temperature structure stability of this coating mould are demonstrated. We can find that the crystallization of t-ZrO₂ as well as the tetragonal to monoclinic phase transformation are, respectively, retarded and impeded owing to the encasement of SiO₂ matrix. While the inhibitive effect of B₂O₃ on crystallization of the SiO₂–ZrO₂–B₂O₃ coating mould is explained. Finally, DD3 single crystal superalloy melt can realize highly undercooled rapid solidification by adopting this coating mould, which further evinces that SiO₂–ZrO₂–B₂O₃ coating mould has an ideal nucleation inhibition for superalloy.     

Influence of the dipping coating procedure on the mechanical strength of soda-lime glass rods

In order to investigate the effect of sol-gel coatings on the mechanical behavior of a high strength glass substrate, HF etched glass rods were used.

Coatings with different compositions (SiO₂, ZrO₂ and 20%ZrO₂---80%SiO₂) and different thicknesses were produced to study the influence of these parameters on strength.

Functions of integral probability versus strength were used to analyze data.

Coated glass rods exhibit higher strength in comparison with uncoated control rods that have undergone the same treatment. It seems evident that there is an effect of composition on strengthening. SiO₂ coated rods displayed higher strength.

A lowering in strength at thickness higher than 0.2 μ was observed, independently of composition.

The effect of a saturated Ca(OH)₂ solution was also studied.     

The influence of the crystallization process on the internal friction of some oxide glasses

The influence of phase separation and crystallization on the internal friction of some oxide glasses is reviewed and discussed. In alkali-containing glasses, the internal friction peak caused by stress-induced diffusion of alkali ions decreases in magnitude and shifts to higher temperature slightly due to phase separation. And in alkali-free glasses phase separation only exerts a minor decrease upon the background of internal friction curves, whereas crystallization influences the internal friction of these glasses more strongly. Because of crystallization, in alkali-containing glasses alkali ions might diffuse in a residual glass phase and a crystal phase, respectively. This might cause corresponding internal friction peaks. And in alkali-free glasses, no evident internal friction peak is observed. However, the author found a high and wide internal friction peak at about 100°C in the crystallized MgO·Al₂O₃·SiO₂·TiO₂ and ZnO·Al₂O₃·SiO₂·ZrO₂ glasses. The peak occurring in the two glasses studied is probably connected with glass crystallization and crystallized crystals.     

SAXS investigations of structure of formation in alcoholic ZrO2---SiO2 solutions

Small-angle X-ray scattering was used to examine in situ formation of ZrO₂---SiO₂ structures in alcoholic solution of tetraethoxysilan (TEOS) as a function of the ratio of ZrO₂ to SiO₂. For the moment of the first measurement (15 min after the preparation) primary particles with R_g ≈ 1.5 nm exist in all investigated mixed gels. These particles aggregated to secondary clusters. The resulting clusters can be described by means of fractal theory, where the determining mechanism of formation is cluster-cluster aggregation (diffusion or chemical limited). The time of gelation is a function of the ZrO₂ concentration. The higher the ZrO₂ concentration in the solution, the faster is the aggregation to secondary clusters. Gelation times were between 170 and 970 h.     

The corrosion of zircon and zirconia refractories by molten glasses

The corrosion of ZrO₂-containing refractories by molten glasses has been investigated experimentally in relation to the compositions of the glasses. For a zircon refractory, zircon crystals contacting the glass decomposed into ZrO₂ crystals and glassy phase at higher temperatures. The decomposition temperature was changed with the glass compositions. Alkali components in the glasses were confirmed to be most corrosive for the zircon refractory. For a ZrO₂ refractory, compositions of the glass-refractory interfaces were nearly saturated with ZrO₂. The corrosion rate of the ZrO₂ refractory was considered to be controlled by the transport rate of zirconium away from the interface.

The concentration of CaO in glasses, as well as that of alkali components, was found to be very effective for increasing the corrosion rate of ZrO₂ refractories.     

Surface modification of a TiO2 film electrode prepared by the sol-gel method and its effect on photoelectrochemical behavior

The surface of a TiO₂ film electrode, about 1 μm thick, prepared by the sol-gel method, was modified by being additionally coated with about 0.1 μm thick TiO₂---SiO₂, TiO₂---ZrO₂ or TiO₂---Al₂O₃ films. The effect of the additional coating on the photoelectrochemical properties of a TiO₂ film electrode was investigated in detail. On addition of the second additive to TiO₂, the flat band potential was shifted toward negative potential for SiO₂ and positive potential for ZrO₂ and Al₂O₃, which is attributed to the change in the point of zero zeta potential (pzzp), not in the electron affinity (EA). However, enhancement in photocurrent was not observed for all the cases.     

Correlation between interfacial structure and c-axis-orientation of LiNbO3 films grown on Si and SiO2 by electron cyclotron resonance plasma sputtering

Thin films of crystalline lithium niobate (LN) grown on Si(1 0 0) and SiO₂ substrates by electron cyclotron resonance plasma sputtering exhibit distinct interfacial structures that strongly affect the orientation of respective films. Growth at 460–600 °C on the Si(1 0 0) surface produced columnar domains of LiNbO₃ with well-oriented c-axes, i.e., normal to the surface. When the SiO₂ substrate was similarly exposed to plasma at temperatures above 500 °C, however, increased diffusion of Li and Nb atoms into the SiO₂ film was seen and this led to an LN–SiO₂ alloy interface in which crystal-axis orientations were randomized. This problem was solved by solid-phase crystallization of the deposited film of amorphous LN; the degree of c-axis orientation was then immune to the choice of substrate material.     

Structural difference of surface and sub-surface native oxides of evaporated amorphous silicon

Evaporated amorphous silicon (a-Si) films, oxidized in air or O₂ at room temperature, present two native oxides with different structures. The surface oxide is constructed from SiO₄-tetrahedron structural units with a 110° O---Si---O angle, which is the common structural unit of stable silicon oxides. The internal oxide has a different structure having a 120° O---Si---O angle. The results of molecular orbital (MO) calculations for (SiO₃)^m− and (SiO₄)ⁿ⁻ anionic clusters support the presence of the two stable structures of silicon oxides and also reveal the importance of the ionic character of the oxidized sites.     

Optical third-harmonic generation from some high-index glasses

Optical third-harmonic generation from some high-index glasses was investigated. The highest χ⁽³⁾ was obtained from As₂S₃ glass 2.2 × 10⁻¹² esu/ This value was 100 times higher than that of pure SiO₂ glass and comparable with that of the polymer with monomer-doping, which are known as organic materials with quite high χ⁽³⁾. From the relationship between χ⁽³⁾ and composition, sulfide glasses were found to have higher χ⁽³⁾ than oxide or semiconductor-doped oxide glasses with similar refractive indices.     

TOPCon太阳电池发射极Al2O3/SiNx与SiO2/Al2O3/SiNx叠层膜钝化性能的比较

本文对TOPCon电池发射结的叠层钝化膜进行了研究,对比了3种不同叠层钝化膜(SiO₂/SiN_x、Al₂O₃(1.5 nm)/SiN_x、SiO₂/Al₂O₃(1.5 nm)/SiN_x)的钝化性能。结果表明:Al₂O₃(1.5 nm)/SiN_x的钝化性能优于SiO₂/SiN_x,SiO₂/Al₂O₃(1.5 nm)/SiN_x的钝化水平最佳,隐开路电压均值可达到705 mV。基于Al₂O₃/SiN_x叠层膜研究了Al₂O₃厚度(1.5 nm、3 nm和5 nm)对钝化性能和电池转换效率的影响。当Al₂O₃厚度由1.5 nm增加到3 nm时,钝化性能得到明显提升,隐开路电压均值提高了20 mV,达到707 mV,对应电池的光电转换效率升高了0.23个百分点,与SiO₂/Al₂O₃(1.5 nm)/SiN_x叠层膜电池的转换效率持平。然而,当Al₂O₃厚度继续增加至5 nm时,隐开路电压均值保持不变。因此可以使用Al₂O₃(3 nm)/SiN_x叠层膜代替SiO₂/Al₂O₃(1.5 nm)/SiN_x叠层膜,不仅简化了电池的工艺步骤,而且降低了生产成本。     

Electrical conductivities of mixed cation glasses

The electrical conductivities of (1−x) Li₂O · x BaO · 2 SiO₂, (1−x) Na₂O · x MgO ·2 SiO₂, (1−x) Na₂O · x CaO · SiO₂ and (1−x) Na₂O · x BaO · 2SiO₂ glasses were measured at temperature ranging from room temperature to 450°C. The transport numbers for Na⁺ ion in (1−x) Na₂O · x BaO · 2 SiO₂ glasses were measured. It was found that the alkali ion carried a significant part of the current in these glasses except one that had no alkali ions, and the conductivity decreased markedly as the alkali oxide was substituted by an alkaline earth oxide. The results of conductivity measurements combined with the data hitherto reported on mixed alkali glasses led to the proposal that the so-called mixed alkali effect could be explained on the basis of the independent path model in which it is assumed that cations can move only through vacant sites left by those of the same type.     

Radiation-induced trapping centers in thin silicon dioxide films

In this paper the technological and scientific aspects of radiation-related charge trapping in thin SiO₂ films are reviewed. These films are amorphous in nature and are thermally grown on single crystal silicon substrates serving as the insulating layer in metal-oxide-semiconductor (MOS) capacitors and transistors. The structure and operation of these devices are reviewed with special emphasis on the effect of charges trapped in the oxide. The technical importance of understanding the interaction of ionizing radiation with thin SiO₂ films is illustrated with two practical examples. The first involves the operation of MOS transistors in environments where ionizing radiation is present, leading to an accumulation of positive space charge in the oxide. The second deals with process-induced defects generated by radiation encountered during the fabrication of devices by processes such as electron beam lithography or electron gun metallization. Unannealed traps of this type capture hot electrons producedin the substrate during the operation of the MOS transistor. In both these examples, the charging of the oxide results in instabilities which degrade operation.

Its sensitivity to charge trapped in the insulator makes the MOS system an ideal vehicle for scientific study of these phenomena. The basic techniques for characterizing the density, capture cross-sections, and location are briefly discussed and applied to the problem of radiation-induced defects in thin SiO₂ films. Ionizing radiation is shown to interact with the SiO₂ in two modes. In the first it supplies carriers to fill pre-existing hole traps at the interfaces. In the second it creates electron and hole traps in the bulk of the thin film. These latter defects are in a neutral state after irradiation and are detectable only when either electrons or holes are subsequently injected into the oxide. The capture cross-sections, trap densities and location of these centers in the film are presented. The annealing treatments required to remove these traps from aluminium and polysilicon gate devices are also discussed. The number traps produced by an incident 25 KV electron beam is found to depend weakly on the dosage. A dipolar defect, produced by the ionizing radiation, seems to explain the behavior of the neutral centers.     

Feasibility of the electrical characterization of single SiO2 breakdown spots using C-AFM

Due to the progressive scaling down of MOS devices, new methods are required to study the failure mechanisms of the gate oxide in a nanometer range. In this work, an atomic force microscope equipped with a conductive tip and a sensitive preamplifier has been used to study the electrical properties and degradation dynamics of single breakdown spots of 3–6 nm SiO₂ films on a nanometer scale. With this purpose, voltage ramps over areas of 30–50 nm² (of the order of the breakdown spot area) have been repeatedly applied to induce the degradation of the SiO₂ films. Similar results to those observed with conventional tests (such as the switching between two states of well-defined conductivity) have been measured with this technique. As a conclusion, our results point out the conductive atomic force microscope as a tool for the analysis of the electrical properties and degradation of single breakdown spots.     

Oscillator strength of the infrared absorption band near 1080 cm in SiO2 films

It has been well known that the absorption maximum of the peak near 1080 cm⁻¹ in amorphous SiO₂ films shifts continuously with variation of thickness and properties such as stress. This is a first report on the oscillator strength of the absorption against frequency at the absorption maximum. SiO₂ films on silicon wafers were prepared by thermal growth in either dry O₂ or an O₂/H₂ mixture or liquid-phase deposition in HF saturated with silica gel. The oscillator strength continuously decreased from 1×10⁻⁴ down to 1×10⁻⁵ with the frequency shift from 1099 to 1063 cm⁻¹.     

Vibrational spectroscopy of LaBSiO5 glass and glass–crystal composites

Infrared (IR) reflectivity and Raman scattering spectra of LaBSiO₅ glass and glass–crystal composites were studied in the temperature range 25–260 °C. Using an analogy with the LaBGeO₅ crystal it was possible to assign the main spectral features of the LaBSiO₅ glass and glass–crystal composites. The BO₄ chain arrangement and the bending vibrations of SiO₄ are influenced by the loss of the long-range order in the glass whereas the stretching vibrations of the SiO₄ groups are practically unaffected. The structural disorder in LaBSiO₅ crystallites is caused by rotation of BO₄ tetrahedra.     

An infrared study of crystallization in sodium-disilicate glasses containing iron oxides

The infrared absorption spectra of sodium-disilicate glasses containing various amounts of Fe₂O₃ ([Na₂O · 2 SiO₂]_1−x [Fe₂O₃]_x, where X = 0.05, 0.1 and 0.2) were investigated in the wavenumber range from 200–2000 cm⁻¹. The addition of Fe₂O₃ to the sodium-disilicate glass does not seem to introduce any new absorption band as compared with the spectrum of a pure sodium-disilicate glass; nevertheless, a general shift of the existing absorption bands toward lower wavenumbers is observed. The amount of shift is, in fact, proportional to the content of Fe₂O₃ in the glass. This observation is consistent with the recently proposed structural model for the bonding of Fe³⁺ ions in the iron-sodium-silicate glass system.

Annealing of 20 mol% iron oxide glasses at 550 and 580°C produced an extra sharp infrared absorption peak at about 610 cm⁻¹ wavenumber. This new peak is believed to be related to the crystallized particles of the glass as concluded from both a scanning electron micrograph and an electron diffraction pattern.     

Effects of rapid thermal treatments on the electrical properties of thin SiO2 gate oxide for DRAM p-channel MOS transistors

Silicon oxide has been grown by rapid thermal processing. The growth rate, in the range of very thin films (<10 nm), has been studied as a function of the oxidation temperature. Combined films composed by conventional thermal silicon oxide growth over SiO₂ passivation layer deposited by rapid thermal processing onto Si(1 0 0) substrates have been used as gate oxide of p-channel metal-oxide semiconductor (p-MOS) transistors of dynamic random access memory (DRAM). The effect of rapid thermal annealing treatments on these films has also been experimented. Improvements in the electrical performances of transistors have been observed.